So You Want to Build a Monster (a guide for DMs)

[PhoenixPhyre]

So You Want to Build a Monster
This is intended to be a helpful look at the mechanics and thematics of creating a balanced, engaging creature for play in D&D 5e. Suggestions, criticisms, and questions are welcome. I don't pretend to be an expert. The Excel file in my signature has all the data I'm pulling from, including most of the tables.

http://www.admiralbenbo.org/images/creatures/monster3.jpg

The role of monsters in D&D

By monster, I mean any NPC that is likely to meet the PCs in combat. You rarely need to stat up the village blacksmith or the inkeeper as full creatures but you do need to know how that goblin or that enemy mage will act in combat.

Monsters are foils to the PCs; they have different but complementary roles. For one thing, there generally are a lot more monsters than PCs in any given area. For another, only a small fraction of monsters live beyond a single combat. Recurring NPCs are relatively rare by comparison. On the other hand, PCs are expected to undergo attrition over the course of multiple fights between long rests. This means that monsters, in general, must have lower nova power than a PC--there's no resource management minigame for monsters. Because PCs have significant nova potential,monsters also tend to have higher health to allow for combats longer than a single round.

In addition, the DM has to be able to handle a bunch of monsters simultaneously, while each player only handles their PC. This, coupled with the throw-away nature of monsters generally, makes monsters out to be much less complex than PCs. PCs can have lots of moving parts, resource pools, recovery mechanics, non-combat ribbons, etc. Monsters much less so.

In fact, the non-combat part of most monsters is almost completely up to the DM in 5e. Do you want that evil vizer to be great at persuading the king? He is, you don't need to give him explicit permission slips (features) that let him do that. The blacksmith can simply make things; no need for 52 ranks in Craft Weapons (and the concommitant levels and combat potential).

The last difference is one of optimization. Don't fall into the trap of over-optimizing your monsters against the players. D&D should not be antagonistic, with the DM trying to "win" vs the players or vice versa. You control the world--try to make it as organic-seeming as possible. This means having monsters with flaws, people who do sub-optimal things (or who learn bad but thematic spells, for example). Colorful and easy to run are much more important attributes than are perfect tactics or optimized builds. 5e is loose enough, with few enough game-breaking tactics and builds, that you rarely need to do such things. Good tactics certainly help in an encounter, as does good terrain, but the most important thing is having fun. Know your players--if they want difficult tactical combats, give it to them. If they want colorful descriptions but don't care about always being on the edge of death, give that to them. Etc. You win (as does everyone) when people have fun. Each group's fun will be different.

What makes a good monster?

As I see it, the characteristics of a good monster are these (in no particular order):


Easy to use. Complicated monsters with lots of moving parts will either not use those parts (meaning you wasted your time adding and balancing them) or will take lots of table time (slowing things down and boring players). Except for legendary solo monsters, remember that you're going to be running multiples of most of these monsters (or groups of 3-8 total creatures normally). Contrary to common belief, adding spells to a monster doesn't make them more interesting. It just takes more time and brain space to run, leading to worse tactics.
Thematic. Creatures should have strong thematics that link them to a place in the world. A ice-and-snow creature in the middle of a barren desert is unlikely; a massive flying bird underground is also a bit odd. Same goes for abilities--your descriptions should hint at the strengths and weaknesses of the creature. Creatures covered in massive armor plates or scales should show those; things without mouths shouldn't have a bite attack. And the list goes on. Tactics, capabilities, and descriptions should all work together.
Properly balanced. Glass cannon PCs can work. Glass cannon monsters rarely do--this edition doesn't handle rocket tag (first one to land a blow wins) combat very well. Same goes for the reverse--a wall of meat that doesn't do much is pretty boring (this is often called padded sumo combat). Monsters tend to have more health than a comparable PC but lower burst damage output. Being dropped to 0 HP right out of the gate with no chance of response is a bad outcome for many players--you end up spending combat doing nothing. Same goes for hard CC--the player gets to spend their turns doing nothing and watching instead of playing. Favor abilities that hinder PCs instead of just no-selling/stopping them. Same goes for damage resistance vs immunity--immunity should be pretty rare and very thematic. Resistance is fine, however (basically acting as a health buffer).


What's to come?
Part 2: Modifying Existing Monsters covers ways you can alter existing stat blocks instead of starting from scratch.

Part 3: From Scratch covers the steps needed to make good monsters from the ground up, including using PC classes.

Appendix A: Traits covers the published traits and their effect on CR and on balance generally.

Appendix B: Templates gives a small list of templates--bundles of traits and abilities you can give monsters to enforce a theme. Some are from the published books, others are homebrew.

Appendix C: Encounters--Terrain and encounter-building suggestions.


According to the Dungeon Master's Guide (DMG), there are four categories of combat encounters.

Easy encounters pose only minimal threat. At most, a couple party members might lose some HP. No significant resource expenditure--no short-rest/long-rest dependent resources or consumable items--unless the party has had many such since the last rest. A party should be able to handle 3-4 of these before needing a short rest, for a total of 8-10 per adventuring day without difficulty.

Medium encounters generally require the use of some resource--a spell slot or two, maybe a rage, maybe a healing potion. Still, no character should be in significant danger of being dropped to 0 HP outside of extreme bad luck (chain crits). An average party can handle 2-3 of these between each short rest, for 6-8 total in an adventuring day.

Hard encounters run a significant risk of dropping a character to 0 HP. The chance of actually killing a party member is slight, however. Either good tactics, very good luck, or significant resource expenditure will be needed. A party can usually take 1-2 per short rest at most, for 4-5 per adventuring day. Even then, the last few will be tight depending on luck and party composition.

Deadly encounters run a significant risk of killing one or more characters. Multiple characters will probably be reduced to 0 HP at least once, and there is a small chance of a TPK. More than 2 of these per adventuring day is pushing it.

To these four we might as well add Deadly++ (Boss) encounters. These are the end-of-campaign fights where the party must go all-out to kill or be killed. Having more than one of these per day (or having one of these at the end of a long day of regular fights) risks TPK (and severe WTF looks). These should be designed to allow players to dump everything into a damage nova.



What is CR and how do you calculate it?
Challenge Rating (CR) is a numerical indication of the approximate threat posed by an enemy. More precisely, it estimates how low of a level of a party it is an appropriate challenge for.

As a very imprecise measure, it mainly concentrates on two separate factors--offense and defense. A creature with a strong offense deals significant (relative to average PC health) damage per round; a creature with strong defense can last several rounds against an average party. As such, non-damaging abilities that do not increase survivability aren't factored into CR at all. The five factors that go into calculating CR are


Average Hit Points (HP)
Armor class (with a secondary contribution from proficient saving throws) (AC)
Average Damage per Round (DPR)
Attack bonus (or saving throw DC depending on main offense method) (ATK)
Traits or abilities that affect one of the first four factors. These show up as modifiers on the appropriate factor(s).


Calculating CR
CR is calculated as the mean of two parts: offensive CR (oCR) and defensive CR (dCR). In turn, oCR depends on DPR and ATK, while dCR depends on HP and AC.

Offensive CR
Calculating oCR depends on calculating DPR. This is the most fiddly and difficult part of the entire calculation. An important part is that this DPR represents a maximum average DPR, a ceiling on the damage output. Here are some rules:

Plan out the first three rounds of a fight, trying to maximize the damage dealt.
Assume all attacks hit and deal average damage.
Include spells or other special abilities (like breath weapons) if they deal more damage than standard attacks. Assume that AoE abilities hit two targets and that both targets fail their saves and take average damage.
Include all relevant traits (noted in the Traits section).


Once you have calculated the DPR, look at the table on page 274 of the DMG and find that DPR number in the Damage/Round column. The base oCR is the CR listed for that row. Also note the Attack Bonus and Save DC columns for that row--these are the guidelines for those numbers.

Next, consider how the creature attacks. If it's mostly physical, use the Attack Bonus number; otherwise use the save DC. Once adjusted for traits, this is the creature's ATK.

Take the difference between the creature's ATK and the guidelines and calculate the oCR adjustment = (ATK - guideline)/2. The final oCR = base + adjustment.


Consider the Hobgoblin. Its basic attack routine involves a longsword attack for 5 damage; adding in the Martial Advantage trait (which adds its value, 7 in this case) to DPR gives a DPR of 12. This correlates to a base oCR of 1.0. It has an attack bonus of +3, which is right on for that CR, so the adjustment is 0. Thus, the final offensive CR is 1.0.


Defensive CR
The dCR is easier. First, adjust the HP and AC for defensive traits. Note that if the creature has three or more proficient saving throws, adjust the AC by +2; +4 for five or six proficient saving throws. Then find the adjusted HP of the monster in the DMG table and note the CR and the AC given for that row. Like the adjustment to oCR, the adjustment to dCR is given by half the difference--dCR adjustment = (AC - guidline)/2--and the final dCR by the sum of the base and the adjustment.


Considering the Imp. Magic resistance grants it +2 AC; having resistance to non-magical BPS damage grants it +100% HP. As a result, it has 20 effective HP and an adjusted AC of 15. Looking at the table, 20 HP is dCR 1/8; this is adjusted by (15-13)/2 = 1, for a final dCR of 1.125.


Final CR
The formal CR is calculated as (dCR + oCR)/2. What about rounding? The DMG says to round to the nearest CR step (usually integers), but I'm not so sure. The MM monsters suggest that there is more thought involved here--many of them are off from their calculated CRs by several steps.

A few considerations--
Damage output: Consider a weak player character (a wizard or sorcerer) of level = CR. Would a single round's damage output take such a character from full HP to 0 if everything connects? If so, the CR is too low and should be moved upward until that's no longer true. An example is the Ogre--it deals enough damage to KO a level 1 PC, so it's rounded up to CR 2. A rule of thumb is that for tier 1 or two, Level = CR + 1 is the earliest you could expect to run into multiple creatures of that CR and have a non-deadly fight. Since hard fights should (individually) have a low risk of permanent character death, a creature that can one-round KO a PC is significantly too dangerous (accounting for crits).

Abilities requiring high-level counters: Low level parties have few means of overcoming certain abilities. For example, immunity to low-level spells. Other examples include afflictions that permanently remove a character from play (like petrification) that require high-level spells (e.g. greater restoration) to remove.

Low Health: Because CR is an average, some monsters seem like a threat but aren't such in practice because they can be obliterated with ease. For example, the goblin has a calculated CR of 2 or more if it can hide consistently. On the other hand, it can't always do so and can be one-shot by most damage-focused level one characters on a good hit (7 HP ~ 1d8 + 2). This makes them glass cannons--able to hurt the party a bit but unlikely to survive very long. If a creature can be killed in a single round (or worse, attack) by a level appropriate PC (level CR + 1 or CR + 3 for T3/T4), especially if that wouldn't cost any resources beyond an action, its CR is probably too high. Adjust downward until this is no longer true.

For the first type (e.g. a rakshasa's immunity to spells of levels 5 or below), the minimum CR is in the appropriate tier (T3, in this case) and the other statistics can be adjusted to suit. The rakshasa is only a CR 5 threat without the magic immunity; with it, it's CR 13 to give magic users a chance against it. Another example would be the Archmage NPC--it's a CR 7 threat that is bumped up to CR 12 because of its globe of invulnerability spell (and the ability to cast 9th level spells--giving it a high level damaging spell drastically changes the threat picture).

For the second case, make sure that the ability requires multiple failed saves at low DCs to be completely removed from play and bump up the CR by one or two. The basilisk is only CR 2 by calculations, but is CR 3 due to the petrifying gaze ability.

If none of the considerations hold, round to the nearest CR step. Then adjust after play-testing (covered elsewhere).

[PhoenixPhyre]

Part 2: Modifying Existing Monsters
Lazy DMs know that theft is often best. :smallcool:

Refluffing
Not all changes need to be mechanical. I've gotten great use out of simply describing the same stat block in multiple ways. One key enemy of my setting are the Awakeners--beings from Beyond reality that break down reality and try to destroy things. Physically, the common soldiers appear as warped reflections of humanoids, but as if made out of wax that was partially melted and then hardened. Joints in strange places, long spindly arms, etc. They often grow long claws and piercing teeth and use chaotic magic. How did I run them? As slaad (mostly the lower ones). I just described them as above.

This does have its limits--once you find yourself adding or dropping traits to fit the description better, you're probably at the point where you want to formally modify the creature as described below.

Changing existing monsters
http://www.admiralbenbo.org/images/creatures/Monster1.jpg
Concept art from The Incredible Adventures Of Van Helsing (https://en.wikipedia.org/wiki/The_Incredible_Adventures_of_Van_Helsing)

One of the easiest ways (beyond simple re-fluffing) to create a new creature is by making small changes to existing published ones.

There are several ways one might do this:
Changing HP
Making a buffed version of a creature can be as simple as using maximum HP instead of average. If doing this increases the HP by more than 30 (90 above CR 19), increase the CR by 1 for every multiple of 30 (this is a change in defensive CR of 2). Note that for creatures with defensive traits that modify effective HP (especially things like resistances that provide HP multipliers) this is a dramatic understatement. If a low-CR creature has multiple resistances, the threshold for a change in CR is about 15 (to account for the doubling of effective HP due to resistances) instead.

The same goes for decreases in HP. You can represent an already wounded monster by having it start below average HP. Unless you dramatically change its health, this usually has little effect on CR and might not be noticeable in play.

Rolling the creature's HP (instead of taking the average) has no substantive effect on CR since the bell curve for NdM is strongly peaked above two or three HD. It is a good (although labor intensive without a dice-roller) method of making each goblin be somewhat different.
Adding HD
Unlike in previous editions, the number of hit dice is completely arbitrary in this edition. It has no effect on anything except by changing the number of hit points the creature has.

By convention, the size of a hit die is set by the creature's size, not its class or type. The following table summarizes the information:


Size Category
Hit Die
Average HP/die


Tiny
d4
2.5


Small
d6
3.5


Medium
d8
4.5


Large
d10
5.5


Huge
d12
6.5


Gargantuan
d20
10.5



Average hit points are calculated as HD x (Average + Constitution modifier).

When adding PC class levels, add one HD per level, but use the size category's HD size, not the class's HD size. Creatures shouldn't have mixed-size HD.

Adding or changing Traits
There are many traits that can be added without changing the CR; others directly change CR. In all cases the traits should reflect the thematics of the monster. A cringing, cowardly race (like goblins) shouldn't have a trait that grants immunity to fear. Sneaky monsters should have traits that reflect that (and vice versa--creatures with sneaky traits should probably use them). Note that you can come up with new names and descriptions for traits--as long as the mechanical effect does not change there's no change in CR effect. For example, the various Yuan-ti in VGtM have different "fang" traits that all grant a certain amount of damage (of various types) once per turn. This is effectively a modified sneak attack, but the name and the damage type are evocative of the theme of the creature. Another example is the Angelic Weapons trait (add extra weapon dice)--bugbears have the same (mechanical) trait but it's called Brute for them to reflect the differences in theme.

For humanoid (any race) monsters, there is a table in the DMG that includes all the PHB races (plus a few) with modifications. Those generally don't modify CR.

See Appendix A (Traits) for a complete listing of traits from the MM, DMG, and Volo's Guide.

Changing weapons
Monster weapons do not necessarily follow the same detailed rules as players' weapons do. The biggest difference is in what stat modifier is used. While generally melee weapons use Strength and ranged ones use Dexterity, this pattern does not hold for all creatures (especially non-humanoid ones). Natural attacks (claws, bites, etc.) can use whichever modifier is better (like a finesse weapon).

For ease of play, you can use the same modifier for all attacks unless you want to signal a weakness.

Damage dice are also somewhat arbitrary, at least for natural weapons. Manufactured weapons (those found on the PHB table) tend to follow a strict pattern--each size category larger than Medium increase the number of dice by 1; tiny weapons deal 1 damage.

As general rules for natural weapons (all for medium creatures):

Claw attacks (singular) deal d6s of slashing damage and a creature gets one per claw.
Claws (plural) deal multiples of 2d6 (d4s for small creatures) as slashing damage and a creature gets one such attack. The books are inconsistent about when to give which one, but generally beasts do claws, clawed intelligent creatures do separate claw attacks.
Bites deal d8s of piercing damage (1d8 for most medium/large creatures) but might additionally include poison or other damage types. If a creature has a disease, the bite is most likely to transmit that disease. Bonus action attacks (from pounces or grapples) tend to be bites
Tails tend to deal varying amounts of damage. This is also a poison delivery mechanism for some. Tails of large creatures may have knock-back or proning effects.
Hooves, stomps and slams (unarmed, unskilled hand attacks) tend to deal bludgeoning damage, usually in multiples of 1d8.


An increase in DPR of about 10 increases the CR by 1.

Remember to modify the Multiattack action (if present) to account for the new weapons.

Making a solo monster from an existing monster
The bare minimum needed to make a good solo monster is legendary actions. At higher CRs (T3 and T4, mostly), legendary resistances and lair actions become important.

Legendary actions (LA) partially correct for the big killer--action economy. An average party has 4 players, so that's 4 actions to the solo monster's 1. As a result, most legendary creatures have 3 LA uses per round (but only one per turn). These occur after a player's turn and are recharged at the beginning of the monster's turn. A good pattern is to add the following options:


A basic attack (not a multiattack)--a bite, a claw, a stomp, a spell ray.
A movement option
A mixed/complex option that uses 2 LA uses.


Spellcasting tends to cost 3 LA uses.

Note that this usually dramatically increases the monster's DPR (since they get 3 more basic attacks per round). The percentage increase depends on how many attacks it makes--this effect is largest at low CR when things are attacking once per round (being a 300% increase in DPR).


Crushbreath is a massive ogre who even other ogres are afraid of. His breath is especially bad.

Changes:

Add Stench trait: Creatures that start their turn within 5 feet must succed on a DC 14 Constitution saving throw or be poisoned for 1 minute. Poisoned creatures can repeat the saving throw at the end of each of their turns, ending the effect on a success. +1 effective AC
Add +2 natural armor due to extra blubber (bringing his AC up to 13, 14 effective)
Add 3 LA uses. (+13x3 = +26 DPR)
Use max HP (91) instead of average (+32 HP). For a bigger challenge (but a more balanced offense vs defense), add a few hit die (+13 HP each if maximized) as well. If you add 2 more HD, his CR goes up by about 1, at which point he's not as (proportionally) dangerous.


Legendary Actions:

Greatclub: Crushbreath makes a Greatclub attack.
Shoulder Charge: Crushbreath moves up to his speed directly at an opponent. If he ends this movement within 5 feet of an opponent, that opponent must make a DC 14 Strength saving throw or be knocked prone.
Spinning Smash (costs 2 uses): Crushbreath swings his greatclub in an circular arc. All creatures within 5 feet of him must make a DC 14 Dexterity save, taking 13 (2d8+4) bludgeoning damage and are knocked back 10 feet on a failure. Creatures that succeed on the save take half damage and are not knocked back.


New CR: base offensive CR = 8, -0.5 for low ATK relative to CR. base defensive CR = 2, no adjustments. Overall CR: 5. This would be a hard challenge for 4 level 3 PCs or a medium for 5 level 3 PCs.

Note that he would be very dangerous to the squishier party members, especially if he focus-fires one with all his legendary actions. An average wizard at that level has 26 HP, so one full round (main + 2 legendary actions) is enough to outright kill such a player if all hit and deal average damage--action + 1 LA to drop the PC to 0 HP, 2 more (both critical hits) to force 3 death saving throw failures. Crushbreath is pretty stupid, though (at INT 5, so he may not think to do that if the party thinks to insult him (which will drive him into a blind tantrum, smashing the first things he can). He's vulnerable to Wisdom saving throw-forcing effects and will die pretty fast if focus-fired, but he hits like a truck.


Adding PC Class Levels
While this is not wrong, it's highly inefficent and produces wide swings in power. Most of the time, what you really want are the emblematic abilities and traits of a class--just go ahead and add them as traits/actions. The only time I'd really consider this is for creatures that adventure with the party for a while.

If you really want to formally add class levels, here are some considerations.

Adding frontloaded classes make for big power swings--one level of barbarian on a melee-type creature is a huge change (worth a few CR), while adding a single level of wizard to anything but the weakest creatures is basically flavor.

Many monsters only fight once per day (against the party) Generally, PC classes are designed to gradually use up resources over the course of an adventuring day. Giving that same power (especially things like paladin's smite) to creatures that will only fight the PCs means that they can nova without fear. This can pose much more threat than intended.

Spell selection matters Some spells and abilities are really annoying to be used against the players. Hard control (banishment, etc), mind control, force cage, things like this lock a player out of the game for an extended period of time. Talk to your party before deploying these against them. Yes, that's assymetric, but so is the role of a DM. They don't have other creatures to play while they have to sit there and watch their party have fun. This is especially true if you target them against the player's weak saves or otherwise seem to be specifically targeting someone.


In parentheses after the description is the mechanical CR effect.


Barbarians (Rage)--Resistance to bludgeoning, piercing, and slashing damage [+100% HP]. Add in Reckless [--] for a berzerker.
Bards (Bardic Inspiration)--Leadership [--], flavored as singing. Spells, mostly support.
Clerics (Channel Divinity)--Chose an appropriate channel divinity for the subclass. Turn/Control Undead is a classic, but only really visible against necromancer PCs. Buffing spells.
Druids (Summoning animals)--Wildshape usually is a waste here, although you can get it to work if you try. Note that NPCs don't get extra health from Wildshape (see the Archdruid NPC for an example). Instead, give them nature-themed battlefield control spells and summoning. [??]
Fighters (Action Surge/Indomitable)--Action Surge (1/day): The creature can take two actions instead of one. [~ +33% DPR]. Indomitable (1x/day): When <name> fails a saving throw, it can reroll but must take the second one. [< +1 AC].
Monks (Unarmed attacks/Flurry of blows)--just give them more, weaker attacks. At high levels, a limited-use stunning strike might make sense.
Rangers (Animal companion)--pair this creature with a beast. Add a trait that allows the beast to attack when the master does.
Rogues (Sneak Attack/Cunning Action)--Give them a few sneak attack dice (2-4 d6). Cunning action (hide) is a major boost [+4 AC/+4 ATK if they can hide consistently].
Sorcerers (Metamagic)--a 1x or 2x/day twin, quicken or highten.
Warlocks (Eldritch Blast)--really, giving them this as a cantrip screams "warlock." Proper descriptions go a long way here as well.
Wizards (sub-class features)--Filch one of the level 2 specialization features. Arcane Ward's a good one, as is Sculpt Spell.

[PhoenixPhyre]

Part 3: Monsters from scratch
Sometimes, you just have to build one from the ground up. Like this one.

http://www.admiralbenbo.org/images/creatures/monster2.jpg

Creating a monster from scratch
There are two approaches here--numbers first and fiction first. I strongly recommend the fiction-first approach.

Numbers First
Here, pick a total CR and the pair of oCR and dCR that average to that CR. Generally, creatures have lower dCR than oCR; this accounts for the relative ease of adding defensive traits. On average, MM and VGtM creatures have around half the health indicated by their total CR but make up for it with other defensive traits and higher AC.

Use the table to extract HP, DPR, ATK, save DC, and AC values. Choose any combination of attacks, stats, etc. that give those numbers (less if you're going to add traits). Add mechanically-relevant traits and check their effect on the final CR.

There. You have a basic monster with no soul. For cannon-fodder that works fine but gets boring pretty fast, especially for important monsters.

Fiction First

First, figure out what kind of creature you want to make and give it a name. Good names are hard, but necessary. They shape how you'll see that creature. Consider its place in the world around you. Where does it live (terrain)? Does it go about in packs? What does it eat? Is it aggressive? Is it intelligent (more than an animal)? Figure out the size category (Tiny, Small, Medium, Large, Huge, or Gargantuan)

Second, figure out a CR target range. This can be very loose, but do you want it to threaten T1 characters (levels 1-4), T2 characters (levels 5-10), T3 characters (11-16), or T4 characters (17-20)? Note that monsters stay relevant for a while--the average threat faced by a T4 group will probably be in the CR 10-12 range. The high CRs (especially those over 20) are mostly reserved for boss-type monsters--legendary solos and non-legendary group fighters.

Now start deciding how the creature's ability scores should look. Is it a wall of meat that can absorb lots of punishment? If so, give it a high Constitution modifier. Is it nimble? Give it a high Dexterity. Is it smart? Give it a high Intelligence. Compare to various creatures--an ogre is STR 19, etc. The one hard cap here is that no ability score should be greater than 30, and only extremely-powerful creatures should break 20. 10 is average--if it's nothing special in either direction, give it a 10. Many (if not most) natural creatures have a decent Wisdom modifier (as in no lower than -1)--imperceptive creatures don't live long.

If a creature should be better than it seems at a certain saving throw, give it a bonus to that saving throw. This is usually the proficiency bonus (from the table for the CR), but just note that it has a bonus for now. You'll clean up the numbers later.

Figure out what the source of its armor class is--manufactured armors use the same table as PCs, but you can add natural armor (things like scales, being hard to hit because it's small, etc.) AC = (armor base or 10) + Dexterity modifier + shield (if present) + natural armor (if present). Adjust until it fits your image right, don't worry about the numbers.

Next is to determine HP: HP = HD x (HD value + Constitution modifier) on average. HD are arbitrary in number, but use the ones given by the size category. Remember that going up 1 size category increases the effect of each HD by 1 (except gargantuan, which adds 5/HD), so bigger (physically) things have fewer HD than smaller things of that same total HP. There is absolutely no direct connection between the number of HD and the CR--the Beholder (CR 13, 180 HP) has 19 HD, the Death Tyrant (CR 14, 187 HP) has 25. But the Beholder has a much higher CON (+4 instead of +2). Total HP is all that matters, not how it's calculated. Monsters don't take short rests (usually), so healing based on HD is rather irrelevant 99% of the time.

Now do the same sort of thing for attacks. Generally, cat-like creatures do both a bite and claws, while dog-like creatures only do a bite. Higher CR creatures tend to do more attacks rather than more damage per attack (at least within the same size category). Generally, a high CR creature should be making 3-4 attacks per round, a low CR creature 1 or 2. Remember that more attacks equals more rolls, and thus more table time. Monsters start making more than one attack much sooner than players do--there is no BAB-like forumla here. Go with what seems right for the creature. The attack bonus can come from either Strength or Dexerity (for melee weapon attacks)--ranged weapons use Dexterity and spell attacks (like a flameskull's fire ray) use one of the mental stats. Always add proficiency (using the table in the DMG).

Adding in non-attack abilities works similarly. I'd recommend looking for an analogous one in the MM or VGtM and copying the wording. This prevents stupid mistakes and loopholes and creates consistency. Note that if an ability doesn't do damage/affect survivability it will not affect CR but still may pose a significant threat. Non-combat abilities generally are free--sprinkle them in wherever appropriate.

Once you have an idea of what type of creature it is (both defenses and offenses), it's time to crunch the numbers. This works exactly the same as modifying another monster--go ahead and re-read the Calculating CR section. If the creature ends up too powerful or too weak for your purposes, adjust the health or the damage until it feels right.

Monsters as PCs
The biggest thing to remember is that CR =/= level. In fact, the correlation between CR and level is very variable, especially for spell-casters. I recommend instead adding evocative traits to a regular NPC stat block. If you insist on going down this road, consider these recommendations.

Have a balance between defense and offense. No one likes being nova'd down from surprise before they can react. Monsters tend to be able to nova more than PCs can (if you're sticking to the appropriate encounter schedule). So either in build or in play, don't go all-out nova.

Make it a real character. Give them strengths and weaknesses--don't build cookie-cutter optimized builds. Real NPCs don't have a magic scroll that lists what spells or feats they can take--they should end up with things associated with their character and past experiences.

Don't bother statting out all the details. Choose a couple skill proficiencies that matter for the character, don't worry about getting one of the formal backgrounds. The features only come up very rarely, and as NPCs they can come up by fiat.

Tier categories
Some traits are common throughout, others come on later.
Tier 1
Resistance to non-magical damage (as well as more than incidental resistances) are rare. These monsters are generally large at biggest, although there are a few huge beasts (dinasaurs, elephants, giant snakes, mostly). Lots of beasts, humanoids, and undead in this tier. At the upper reaches you start getting appreciable numbers of fiends. Wyrmling dragons are the dragons in this tier.

Tier 2
Resistance to non-magical becomes more common. A few legendaries, but still pretty rare. Significant primary spell-casters (other than the very weak acolyte/Priest NPCs) come online at the mid-top of this tier and low into the next one. This is where the vast majority of monsters sit, as these are the work-horse monsters for most campaigns. More large and huge monsters than small or tiny here. Young dragons, most fiends, major undead. "Standard" elementals are low T2.

Tier 3
Pretty much everything's online at this point. Many of the high T3 monsters (CRs 15-16) are starting to become more mini-bosses. Magic resistance is pretty common, as are legendary resistances/actions. Adult dragons, major fiends, and other boss-type monsters here. Beholders.

Tier 4
Just about everything here is legendary or a boss-type (things like the Balor are designed to have buddies around, which is why they don't have legendary actions). Bigger adult dragons, highest-rank fiends.

Epic Tier (21+)
Exclusively legendary, mostly ancient dragons. In fact, only Kraken does not have Legendary Resistances; it still has Legendary Actions.

[PhoenixPhyre]

Appendix A: Monster Traits
This section reviews the various traits and features found in the DMG, the MM, and VGtM. They are categorized into two major groups--those that affect CR calculations directly and those that do not. Spellcasting, both inate and from spell slots, is reviewed separately as it is complicated.

Each trait is written in the following format:

Name: Effect. Description. sample monsters.
Discussion where it is warranted

Trait names in red text deserve DM caution, as they can be tremendously un-fun if used improperly.
Names in blue text are situationally powerful. See the discussion.


These traits do not change the CR of a monster, at least directly.

Amorphous: --. Allows monsters to fit through spaces as small as 1 inch without squeezing. Many oozes.

Amphibious: --. Allows a creature to breath both air and water. Kuo-toa.

Antimagic Suceptibility: --. Creature is incapacitated by antimagic field and must make a Con save against dispel magic or be knocked unconscious for 1 minute. Animated objects
While this is a major vulnerability against a high level party, at the levels where these monsters usually make an appearance, very few have 3rd or higher level spells to spare. Putting this on a higher-CR monster (such as a golem) would probably result in a reduction of effective hit points--possibly by as much as half.

Blind Senses/Echolocation: --. Creatures with this trait cannot use their blindsight while deafened or in situations where smell is useless. Grimlocks, Bats

Chameleon Skin: --. This grants creatures advantage on Dexterity (Hide) checks. Troglodyte
This trait is situationally powerful. Giving it to a creature that also has ambusher would probably warrant raising the effect of that trait by 100% or so.

Change Shape: --. This grants the ability to change into smaller or humanoid shapes without changing statistics. No combat effect. Metallic dragons

Charm: --. Abilities that fit under this (broad) umbrella impose the charmed condition, sometimes for an extended period. Vampires
Many players find long-lasting mind-control effects to be strongly anti-fun, as they lose control of their character's actions for an extended period of time. Proceed with caution. This ability generally has more role-playing application than combat, and is best deployed against other NPCs (in my opinion).

Damage Absorption: --. This trait specifies a damage type and converts incoming damage of that type into healing instead. Golems
While this is powerful, it's also niche and easily averted. If, however, you put it on a creature facing a group where one or more players is strongly dependent on that damage type (naive blaster sorcerers, usually), it can be obnoxious and feel targeted. I recommend keeping this to energy types (as in not bludgeoning, piercing, or slashing) for both thematic and mechanical reasons.

Devil Sight: --. This trait allows the creature to see through (some) magical darkness. Mainly effective against the darkness spell. Devils (duh), although not the Pit Fiend...

Etherealness: --. This trait allows the creature to enter or exit the Ethereal Plane at will. Night Hag, Succubus
This ability is great for a hit-and-run harrasser, but does little in a stand-up fight. If you want a creature that can run away easily, add this. The surprise potential is limited by the fact that most monsters can't handle the party solo. If you put it on a solo-capable monster, it's basically guaranteed surprise and may warrant concern.

False Appearance: --. This trait makes the creature indistinguishable from an inanimate object as long as it doesn't move. Gargoyle, Treant
Like Chameleon Skin, this can guarantee surprise, and so may warrant increasing the effect if you also give the creature ambusher.

Fey Ancestry: --. Exactly the same as the elven trait by this name. Advantage against charm effects, immune to magical sleep.Drow

Flyby: --. Flying creatures with this feature do not incurr Opportunity Attacks when leaving an enemy's reach. Giant Owl, Peryton
Here I'm not sure why this is CR --.

Grappler: --. This grants the owner advantage on attacks against creatures it has grappled. Mimic
Again, I'd expect it to actually raise the attack bonus of a creature. Not sure why it's rated so low, especially in conjunction with a constrict-type ability or an auto-grapple trait/attack.

Hold Breath: --. Not quite amphibious, these creatures can survive out of their element for a set duration. Lizardfolk.

Illumination: --. These creatures are their own light sources. Some can adjust the light level at will, others can't. Flameskull.

Illusory Appearance: --. The little brother of Change Shape, this one can be broken by Intelligence (Investigation) checks or by touch. Still no direct combat application. Green Hag.

Immutable Form: --. Immunity to any spell or effect that would change the creature's form. Golems.
Basically stops polymorph in its offensive mode. Very niche.

Incorporeal Movement: --. Creatures with this trait can move through obstacles and creatures for free, but take damage if they end their turn in obstructed spaces. Ghost
This can be strong in a hit-and-run scenario where the creature moves out of total cover, attacks, then moves back into cover. If coupled with Nimble Escape (disengage as a bonus action), it can drastically increase the creature's effective health.[/B]

Inscrutable: --. Immune to effects that read minds; attempts to use Wisdom (Insight) against it are at disadvantage. No direct combat application. Sphinx

Keen Senses: --. Grants advantage on Wisdom (Perception) checks using one or more of smell, hearing or sight (which ones, particularly, varies between monsters). Hell Hound, many beasts
Great for guard dogs. Less effective in combat, hence the no-CR effect rating. Foils stealthers pretty well if used right, though.

Labyrinthine Recall: -- The creature can always recall any path it has traveled. Minotaur
I find it hard to create a situation where this trait is more than pure thematics.

Leadership: --. As an action, the creature can add 1d4 to the attack rolls or saving throws of allies within 30 feet. Basically a limited, non-magical bless effect. Hobgoblin Captain, Knight
This would be better if it didn't take an action to set up. Giving it out as a Legendary Action or a no-action trait would be quite strong, adding 2.5 to all saving throws and attack rolls. I'd rate it as adding ~1 to the CR of each allied creature (0.5 for each of the attacks and saves).

Life Drain: --. This action reduces the maximum hit points of a creature by the amount of damage dealt. Some versions heal the user as well. Wight, Wraith
Creatures with this attack as part of their "best sequence" generally have low DPR and/or cannot use this in their multiattack sequence. Be extremely wary of giving this to a creature with high-damage attacks or adding it to multiattack features, especially at low levels. And absolutely don't add it to a Hydra's bite or a Maralith's sword attack. No, really.

Light Sensitivity/Sunlight Sensitivity: --. These cause the creature to have disadvantage on attack rolls and ability checks in either any bright light or in any bright light caused by sunlight. Light sensitivity is a stronger disadvantage--even a torch provides some bright light. Shadows (Light), Kobolds (Daylight)
On a purely nocturnal creature, or an underground-dweller, these merely change tactics and allow interesting exploits. On a creature that goes into the daylight frequently, they make little sense. Best to avoid them in those cases. Creatures with this trait should probably also have better senses for the dark (at least darkvision).

Magic Weapons: --. These creatures' weapon attacks count as magic. Very few player abilities (stoneskin is the only one I can think of) care about this at all. Balor.

Mimicry: --. This trait allows a creature to mimic sounds it has heard (possibly drawing the players into a trap). Kenku.

Otherworldly Perception: --. This trait allows the creature to sense the presence of invisible or ethereal creatures within 30 feet and can pinpoint them if they're moving. Kuo-toa.
Normally, this is very niche. Against a magic-heavy, stealth-heavy party (especially if they are counting on invisibility and surprise) it can be powerful. Does nothing against non-magical stealth, however.


Reactive: --. This allows the creature to take one reaction per turn, not per round. Marilith.
Coupled with an ability like the Marilith's Parry (+5 to AC vs one melee attack), it's a boost. Similarly, if the creature has many things it can do with its reaction it becomes strong. Best used IMO to make a creature very sticky in conjunction with appropriate OA granting abilities.


Read Thoughts: --. Allows the creature to read the thoughts of a target. Also grants advantage on Wisdom (Insight) and Charisma (Deception, Intimidation, and Persuasion) checks against said target. Doppleganger.

Reckless: --. Just like the Barbarian's Reckless Attack feature. Advantage on attacks that round; opponents have advantage on attacks vs the creature. Minotaur.
Unlike most costless traits, this one has a clear cost and benefit. Advantage is worth ~+4 to ATK; the drawback is ~-4 AC (based on how other similar abilities are statted). In a CR calculation, this will cancel out for a net zero. If, however, the creature has devistating attack abilities (like a heavy life drain), adding this trait gives them a much better chance of landing those attacks (which increases their power).

Redirect Attack: --. This ability allows the creature to swap places with another ally within 5 feet when targeted with an attack. The ally becomes the target instead. Goblin Boss.
This is great for those bosses who like to use living shields (and have no care for the lives of their allies). It becomes useless if there aren't any mooks adjacent, though. One idea would be to give it to a mage with a shield guardian. Combining this and reactive...The downside is that it only works on one attack per reaction and characters can move between attacks. Hence it's most powerful at low levels, before extra attack comes fully online.

Reel: --. The creature can pull any grappled targets up to 25 feet straight to it as an action. Only useful if the creature also has a long-range grapple ability. Roper.

Rejuvination: --. The creature, once killed, comes back to life after a significant period (ie. hours or days). Usually has a "unless X happens" ending clause. Lich.
Great for making a boss that just won't stay dead. No direct combat use, though. Flameskulls are 1 hour, lich-types are 1d10 days.

Slippery: --. The creature has advantage on rolls to escape grapples. Kuo-toa.

B]Spider Climb[/B]: --. The creature can climb any surface without a check and without needing to use hands. This works even upside down. Spiders, Ettercap.
Can be strong if used indoors with high ceilings or walls on a creature with strong ranged attacks. Even stronger if the party is mostly melee-dependent. Otherwise niche.

Standing Leap: --. The creature can jump as if it had a running start from stationary. Bullywug.

Steadfast: --. The creature cannot be frightened if it can see another ally within 30 feet. Bearded Devil.

Sure-footed: --. The creature has advantage against being knocked prone. Dao.

Teleport: --. Specifically tactical teleport abilities as opposed to the long-range teleport spell. Balor, Blink Dog.

Terrain Camouflage: --. The creature has advantage on Dexterity (Stealth) checks to hide in the chosen terrain. Yeti.

Tunneler: --. Leaves lasting tunnels behind it when it burrows. Umber Hulk.

Turn Immunity/Turn Resistance: --. Reduces the chances that Turn Undead will work. Revenant (immunity), Lich (resistance).

Two Heads: --. Advantage on Wisdom(Perception) and on saves vs blinded, charmed, deafened, frightened, stunned, and being knocked unconscious. Makes sense only rarely. Ettin.

Web Sense: --. Can pinpoint the location of any creature touching the same web as it. Spiders.

Web Walker: --. Unaffected by difficult terrain caused by webbing. Spiders.



These traits have CR effects spelled out in the DMG. DPR = Damage per Round. ATK = attack bonus.

Aggressive: +2 DPR. Bonus action dash, but only toward an enemy. Orcs.

Ambusher/Slayer: +1 ATK. Advantage against surprised targets. Useful primarily in conjuncion with high stealth or other abilities that allow surprise more frequently. Although the two have different names, they have the same text. Bugbears

Angelic Weapons/Brute: +X damage per attack. These add damage dice on weapon hits. X is the average amount added (7 for 2d6, for example). Angels, Bugbears
Does little on primary spell-casters, but increases DPR by X * number of attacks/round for weapon users. Usually included in the attacks for pre-written stat-blocks.

Avoidance/Evasion: +1 AC. Evasion is just like the rogue's ability; Avoidance is an upgrade granting the same effect on all saves, not just Dexterity ones. Demilich (avoidance), Master Thief (evasion).
Seems to assume that those saves are infrequent. Against a save-heavy party, this might not be true. This is synergistic with high saves. Be careful.

Blood Frenzy: +4 ATK. Advantage on all attacks vs creatures without full health (which is many/most of them). Sahuagain.

Breath Weapon: +2X/3 DPR. X is the average damage amount. Assume it will be used once, hit two people, and both fail their saves. Dragons.
Non-damaging breath weapons are harder to assess, but RoT assign them damage equal to a dragon of similar CR.

Charge/Dive: +X/3 DPR. Deals X additional damage when it hits with a specific attack after movement. Assume it will happen once during the 3 round average. Centaur (charge).

Constrict: +1 AC. The AC boon comes from imposing the restrained condition on one creature. This also applies to any ability that has the same effect--any grapple + restrained trait or ability should get this +1. Constrictor Snake.

Damage Transfer: +100% HP, +HP/3 DPR. This ability means that while attached to another creature, the owner takes half damage and the other half is transferred to the unwilling host. Cloaker.

Death Burst: +2X/3 DPR. When reduced to 0 HP, explode and force save vs X damage. Assume it will hit 2 creatures and they'll fail their saves. Applies to any "explode on death" ability that deals damage. Mephits, Magmin.

Elemental Body: +X DPR. When touched, grappled, or struck in melee, the attacker takes X damage. Assume it will get triggered once per round. Also applies to any other thorns-type ability. Azer, Remorhaz.

Enlarge: +X DPR. As the spell; X usually equals 1d4. Duergar.

Fiendish Blessing/Psychic Defense: +MOD AC. The first is +CHA (always), the second is +WIS (when unarmored and no shield). Cambion, Githzerai Monk.

Frightful Presence/Horrifying Visage/Fear Aura: +25% HP (*). AoE save vs fear. These are all either no-action auras or part of a multiattack routine. The AoE assumes that this reduces the incoming damage by 1/3. (*) Only applies if facing characters under level 10. Legendary Dragons, Ghost, Pit Fiend.
The ghost's version is slightly different (including an ageing effect and requiring a separate action). The banshee also requires a separate action. All the others are high-level effects. All such effects include a "successful saves provide immunity for 24 hours" effect as well. We can extrapolate that a single-target fear effect would give about a 10% increase in health (half as much, rounded down).

Immunity to <type>: +X% HP. Immunity to a damage type. One common damage type or two uncommon damage types are enough to trigger this. Does not stack with more immunities. X depends on tier: 100% in T1 or T2, 50% in T3, 25% in T4.
Deciding where the cut-off is is an art for this one. Be careful of applying them too liberally--instead simply give more hit points and resistance. The burdens of immunities are too unequally distributed across PC classes.

Legendary Resistance: +10*X HP per use. A certain number of guaranteed successes on saves. X = 1 (CR 1-4), 2 (CR 5-10), or 3 (CR 11+). The normal number of uses is 3/LR. Adult and Ancient Dragons.

Magic Resistance: +2 AC. This trait grants the creature advantage on saving throws vs spells or other magical effects. Devils.
This is the most common single trait, especially on fiends and fey. Adding it is an easy way to make beefier monsters, especially against control-heavy parties.

Martial Advantage/Sneak Attack: +X DPR. Similar to the rogue ability. X is the additional damage dealt. Martial advantage does not require finesse weapons and is not triggered by advantage (only by adjacent allies). Hobgoblins.
This is a great way of making a creature feel like a rogue.

Nimble Escape/Cunning Action: +4 AC, +4 ATK (*). Can Disengage or Hide as a bonus action (Cunning Action adds Dash). (*) The bonuses assume the creature will hide each turn. Reduce or eliminate them if the creature is not the type to hide.
This is the single strongest boost of all the defined-cost ones. It grants about +2 CR (+1 from each of the boosts). It is situationally powerful, however. Without adequate terrain or stat support (can't hide in a white room), it becomes useless.

Pack Tactics: +1 ATK. This grants the creature advantage on attack rolls if an ally is adjacent to the target. Wolves.
I think that this is undervalued, especially for mass mob-type creatures. It's useless on solo creatures, but when used by heavy-hitting minion bosses (an ogre with a mob of goblins, for example) it's pretty much permanent advantage and a significant boost. Another time it would be a big boost is on a heavy-hitting ranged creature who has lots of smaller allies. Fewer monster abilities key off of advantage, though, so it's basically more damage.

Parry: +1 AC. Add X to AC against one melee attack that would otherwise hit. Hobgoblin Warlord, Marilith
Oddly, its value does not depend on X (which seems to be 1 at low CR, 3 at medium CR, and 5 at high CR). Value is limited by only working against one attack, and only in melee. From this, I'd give the shield spell a +3 AC rating. It's more of a boost, works against more things (a full round instead of one attack), but is limited by spell slots. Shield at will is the full +5 bonus.

Posession: +100% health. Take over a new body, become untargetable. Kicked out when the body hits 0 HP, when the creature ends it, or certain spells. Ghost.
This can be brutal. Charisma save (often weaker), removes a player from combat until they're dying. Be very careful with this one. It's probably undervalued here.

Pounce: +X/3 DPR. Pounce is like Charge, except it allows an attack as a bonus action (instead of just extra damage). It usually involves a save vs prone effect as well (with the attack contingent on the target being prone). Tiger

Rampage: +2 DPR. Allows the creature to move up to 1/2 speed and make an attack as a bonus action after reducing a creature to 0 HP on its turn. Gnolls.
Volo's Guide introduces Aura of Blood Thirst, which allows each nearby creature with Rampage to make a BA attack each turn. This drastically increases the effect of this trait.

Regeneration: +3X HP. X is the number regenerated per round. Trolls.
Several of these have conditions to end the regeneration (trolls and fire, for example). Those that don't have such conditions also only happen when the creature is above 0 HP. If you want it to not die until <condition> happens, use the troll version. Otherwise, use the slaad version.

As a second note--the power of this trait depends on the tactics used. It becomes strongly more effective if the creature can perform hit-and-run tactics or can break contact effectively. This is especially true against parties that lack good control options or strong ranged attacks.


Relentless/Undead Fortitude: +7X HP. X is the tier associated with the CR: (1: 0-4, 2: 5-10, 3: 11-16, 4:17+). These two traits function slightly differently, but to the same effect. Relentless functions 1x for any attack less than 7X damage that would kill them. Undead Fortitude is a CON save vs 5 + damage, surviving on a success. Wereboars, Boars, Zombies.
The assumption seems to be that it will kick in once for relentless. Zombies will start failing badly if the damage is beyond 7 or so (DC 12). If you tweak the threshold (either amount of damage or the save DC), adjust the bonus accordingly.

Resistance to <type>: +X% health (*). These are your standard resistances--resistance to fire, etc. Only apply it if the creature has several resistances to common types, and it doesn't stack with other resistances. X depends on tier: 100% in T1, 50% in T2, 25% in T3, and 0 in T4.
Where to start counting is a bit fuzzy. I'd apply it if the creature has BPS resistance (against nonmagical) in T1 or T2, but not in T3 or T4 unless it's a low magic world. If magic items are very rare, it probably applies well into T3 if there are lots of martial types in the party. Should it stack with immunities? I think so, as long as it has immunity to common damage types like fire.

Shadow Stealth: +4 AC. These creatures can hide as a bonus action when not in bright light. Shadow Demon.
Although the VGtM trait Shadow Blend (invisibility as a BA in dim light/darkness) is not identical, I figure it should be similar enough for CR purposes).

Stench: +1 AC. Aura--all creatures nearby must save or be poisoned. Immune on a success for 24 hours. Hezrou

Superior Invisibility: +2 AC. Improved invisibility as an action, duration of concentration. Can cast spells/attack while invisible. Pixie
I'm not sure how to rate at-will regular invisibility, since it usually burns an action and breaks if they attack. Great for escaping or for ambushing, not as good in combat since combats go so fast (averaging 3 rounds). Gives disadvantage on opposing attacks, and that's about it.

Surprise Attack: +X/3 DPR. Adds X damage against creatures that are surprised. Bugbear.

Swallow: +2X/3 DPR. Creature can only swallow things 2 size categories lower than it or smaller, and usually must grapple the creature first. Acid damage per round, plus blinded and restrained. CON save vs regurgitation if the swallower takes too much damage in a turn. Behir.

Web: +1 AC. One target is restrained (usually at range), STR save to break free. Spiders.

Wounded Fury: +X/3 DPR. +X damage and advantage on attacks when under a HP certain threshold (20% for quaggoths). Quaggoth.
The assumption is that it gets this on one round of the three. Setting the threshold higher would proportionally increase the damage boost.



These are all my opinions.

Spell Reflection: ???. These creatures can redirect a spell on a successful save or a missed spell attack. I'd probably increase the AC by 1 or 2, but it strongly varies. Flail Snail[/B].

Petrification abilities: ???. Make sure they take multiple, low DC saves to become petrified (at least at lower levels where greater restoration isn't available). Probably worth some extra AC (as it imposes the restrained condition after the first save or disadvantage to close your eyes).

Instant KO abilities: ???. Better have low DCs, especially if they can happen multiple times per encounter.

AoE confusion effects: ???. If they don't have low DCs or don't provide immunity on a success for higher DCs, they get obnoxious fast IMO.

Indomitable: +? HP. A limited version of a legendary resistance (retry instead of auto-success). Maybe worth half as much?



And now for the contentious one. What follows is my opinion only. This applies both to innate and normal spellcasting. The difference is if it's spells N times per day or more traditional spell slots.

Spell Selection Matters: Most "pure" spellcasters in the MM are severely under-CR'd as written. For example, the Archmage NPC (even accounting for the spells he has up at encounter start) has an adjusted dCR of only 4.5 and an adjusted oCR of 9, for an average CR of 7. His nominal CR is 12. The mage NPC is also under-CR, with an average CR of 4ish on nominal CR 6. Giving the archmage [I]meteor swarm instead of time stop and his calculated CR jumps to 13 or so. He also has globe of invulnerability, which lets him ignore any caster of level 10 or lower.

The more focused wizard NPCs from VGtM fare better--the conjurer is right on his CR, for example. Spell selection matters. A lot.

In addition, hard control spells (banishment, maze, etc.) are generally considered to be annoying when used against players in excess. They're powerful, but strongly less fun for many players than effects that diminish their output but leave them free to act. Mind control (dominate person especially) is particularly likely to cause a revolt if overused (or uncautiously used).

Opportunity Cost Matters: giving a creature with otherwise strong abilities some weak spells will have little CR effect--they're unlikely to use them in combat. For purely thematic abilities, consider using innate spellcasting as it's much easier to run and takes up less space.

For spells that fix weaknesses but don't deal direct damage (defensive spells on a glass cannon, mobility or offensive control on a slow bruiser, etc), my rule of thumb is to rate it as granting another round of combat (about a 25% increase in DPR for offensive ones or a 25% increase in health for defensive ones).

Buffs, debuffs, and area control spells can be roughly valued as a damaging spell of their same level (there's a table in the DMG). This probably overstates the value, but it's close enough for CR purposes.

Theme Matters: You are not trying to optimize the NPCs to kill the players (except in rare circumstances). NPCs should have spells that fit their fictional purpose and upbringing. Since non-combat spells are CR-neutral, you can be generous with those. Don't always pick the "optimal" spells--that fire beast shouldn't be creating simulacrulms or casting wall of ice, nor should the air elementals be raising walls of stone.

Ease of Play Matters: Formal spellcasting increases the options (and thus the load on the DM) considerably. Consider giving custom actions that mimic certain thematic spells instead or using innate spellcasting instead of spell slots. Same effect, much less work to run. Recurring NPCs might need more fleshing out, as do those that have narrative value as individuals outside of combat.

Remember that you don't need to give spellcasting levels to be able to cast spells. You can just say "this NPC can cast fireball x/day using CHA" or "Action: Fireball (recharges 5-6), DC 12."



Summoning does not seem to have a fixed CR effect, nor a particular pattern throughout the MM and VGtM. Two (very rough) suggestions for balancing it:

Balance based on DPR: If the creature disappears once the summoner dies, try adding the summoned creature's DPR to 2/3s of the summoner's DPR. The 2/3s accounts for any actions needed to summon them and the possibility of not lasting the full duration.

Balance based on XP: Alternatively, round the summoner's calculated CR down (if not exactly on an existing CR) and add the XP for the summoned creature to the XP for the summoner. Use this XP total to generate the CR for the summoner/summoned pair.

Devils (whose CR tends to be a bit high anyway) don't obey either of these suggestions when using the variant devil summoning option.

[PhoenixPhyre]

Appendix B: Templates

This post is a dumping ground for templates that people have created. Suggest one in the comments and we'll try to build it!


These templates come from one of the Demon Princes of my setting--this particular creature loves to create "art" by twisting living things into new shapes.

Basic rule: if the template grants an attack that the creature already has, it gains an extra use of it (gaining Multiattack if it doesn't already and adding it to that feature if present). If it doesn't have an attack of that type, it gains the attack as described below the table. All these are made at the normal bonus for that attack type (melee/ranged) and use the better of STR and DEX for their bonus damage.

Minor Corruption
Target CR: T1
Creature Type: The type of the creature now becomes Abberation in addition to whatever type it normally had. Spells and effects that can only target abberations can target creatures with this template.
Mutations: Choose 1 at random from the mutations table.

Lesser Corruption
Target CR: T2
Creature Type: The type of the creature becomes Abberation in addition to whatever type it normally had. Spells and effects that can only target abberations can target creatures with this template..
Mutations: Choose 1d4 at random from the mutations table.
Additional Senses: The creature gains Temorsense (60 feet) while standing on corrupted ground.
Immunities and resistance: The creature gains resistance to poison damage (upgrading to immunity if already resistant) and immunity to disease. It also gains vulnerability to necrotic damage.

Greater Corruption
Target CR: T3-T4
Creature Type: The type of the creature becomes Abberation.
Mutations: Choose 1d6 + 1 at random from the mutations table.
Additional Senses: The creature gains Temorsense (60 feet) while standing on corrupted ground.
Immunities and resistance: The creature gains resistance to poison damage (upgrading to immunity if already resistant) and immunity to disease.

Mutations


d20 Result
Name
Effect
CR Change


1
Extra Head
The creature gains Two-headed and a bite attack. Max 1.
~+1 oCR


2
Tentacles
The creature gains a tentacle attack. No max.
~+1 oCR


3
Fast Healing
The creature gains Regeneration as a troll. If it already regenerates, increase the regeneration by 10/round, but gain vulnerability to fire/acid as troll.
+1 CR


4
Sticky
The creature gains the adhesive trait as if it were a mimic, escape DC 13.
--


5
Poison Spit
The target gains the poison spit attack. Max 1.
~+0.5 oCR


6
Armored Hide
The creature gains +2 natural armor bonus but its dexterity is reduced by 2.
+0.5 dCR


7
Sickly
The creature's Constitution score is reduced by 2 (reducing its max HP.
-HD HP


8
Altered Senses
The creature gains blindsight (60 feet) but is blind beyond that distance.
--


9
Stretchy
The creature's melee attacks gain 5 feet of reach.
--


10
Leech
The creature regains hit points equal to half the damage done by its melee attacks.
+1.5xDPR HP (if it uses melee attacks frequently)


11
Bolstered
The creature's HP maximum increases by 30.
+1 CR


12
Altered Body Plan
The creature's movement speed(s) are reduced by 10 feet but all critical hits against it become normal hits.
--


13
Explosive Gases
The creature explodes when reduced to 0 HP. Creatures within 5 feet must make a DC 13 Dexterity saving throw, taking 2d6xTier acid damage on a failure and half damage on a success.
+5xTier DPR


14
Noxious Odor
The creature gains the Stench trait
+0.5 dCR


15
Toxic Blood
When struck by a weapon attack dealing slashing or piercing damage, all creatures within 5 feet must make a DC 12 Constitution saving throw or be poisoned until the end of their next turn.
~0.5 dCR


16
Spiny Carapace
Creatures that hit with melee weapon attacks or grapple the creature take 5 piercing damage.
+5 DPR


17
Mirrored
The creature gains the spell reflection reaction ability of a flail snail (VGtM).
??


18
Brute
The creatures weapon attacks deal an additional die of damage on a hit.
~+25% DPR (roughly)


19
Frenzy
The creature makes an additional attack of its choice each round after being reduced to 50% hit points or below. This lasts until they are incapacitated or healed above 50% health.
+1/3 attack worth of DPR


20
Insanity
The creature choses targets for its abilities at random among all creatures it can see (including allies).
--



Bite Attack
Melee weapon attack. +ATK, reach 5 feet, one creature. Hit: 1d8 + MOD piercing damage.

Tentacle Attack
Melee Weapon Attack. +ATK, reach 10 feet, one creature. Hit: 1d6 + MOD bludgeoning damage and the target is grappled and restrained (escape DC 13). This tentacle cannot grapple anyone else until the grapple ends. Grappled targets take 2d6 bludgeoning damage at the begining of each of their turns.

Poison Spit Attack
Ranged Weapon Attack. +ATK, range 30/60 feet, One target + one other target within 5 feet. Hit: Targets must make a Constitution saving throw (DC 13). On a failed save the target takes 1d4 poison damage for every hit die the attacker has and is poisoned until the end of the creature's next turn. On a successful save the target is not poisoned and take half damage.

[PhoenixPhyre]

Appendix C: Encounter-building

Taking suggestions on what you want to be here or suggested blocks of text. I'm thinking community-generated content :smallbiggrin:.

Terrain and Tactics Matter
Consider a standard 4-PC, level 5 party--a fighter (SnB), a wizard, a cleric, and a rogue (ranged and melee weapons).

Now consider a mid-medium challenge for them--5 hobgoblins (CR 1/2 each) and a hobgoblin captain (CR 3). This clocks in at 2,400 adjusted XP, right between the Medium (2,000 aXP) and Hard (3,000 aXP) breakpoints.

If we run this fight in a flat, featureless plain, starting 120 feet away with the enemies bunched up and wielding their shields (see figure 1), the wizard can fireball them right off the bat (since they can't close to melee within one round, even dashing, and must take an action to doff their shield to ready their longbow). At an average damage of 28 (14 if they save), the hobgoblins will be blown apart instantly, leaving the captain severely hurt. After this, it's an easy fight. Boring for the other three players.

One simple modification would be to have the hobgoblins with their bows out. If they don't win initiative (at a +1 modifier, that's a tossup), the same thing happens. If they do, they get one round of arrows off, dealing (on average) 5 x 5 x 0.6 = 15 damage. Not enough to drop anyone. Then they get fireballed and die. Still boring.

Now consider figure 2. The dotted lines are half-cover (a breastwork or small wall), the solid lines represent a small cliff (10 feet tall) that the two hobgoblins are standing on. The 4 up top have their bows out, the one down below has a shield out. In this scenario, the wizard can only fireball any single group of 2, limiting the casualties and forcing him to make meaningful choices. The hobgoblins will get to use their Martial advantage trait (extra damage when an ally is next to the target), putting more pressure on the PCs. The rogue can use his movement advantage to get up closer, letting him flank the archers better while the cleric and the fighter deal with the captain.

Adding in trees or rocks (not shown) for cover makes it an even better fight--the party can take cover and so can the monsters.


https://www.admiralbenbo.org/images/maps/Terrain.png

[Jama7301]

Dang, there's going to be a lot of information here. :smalleek:

[PhoenixPhyre]

Dang, there's going to be a lot of information here. :smalleek:

The last two spots are pretty aspirational and a dumping ground for anything anyone wants to contribute. The meat is up, so commenting can begin.

[Waterdeep Merch]

This is pretty cool! Going over all of the unspoken rules for monster building is going to be particularly excellent for new DM's. I have a few in mind I'll point here.

[PhoenixPhyre]

This is pretty cool! Going over all of the unspoken rules for monster building is going to be particularly excellent for new DM's. I have a few in mind I'll point here.

Please do!

[Nidgit]

It's be nice for you to add pictures or something to break up the text visually. Most guides are largely composed of lists with literal color commentary but this one, kind of by nature, is all paragraphs. It's a bit foreboding to look at.

[PhoenixPhyre]

It's be nice for you to add pictures or something to break up the text visually. Most guides are largely composed of lists with literal color commentary but this one, kind of by nature, is all paragraphs. It's a bit foreboding to look at.

I'd love suggestions for such. I'm pretty word-oriented myself, so I have a hard time finding effective pictures. I have the ability to host them on a server I run, so where they're from isn't as important as getting links to them.

[Nidgit]

I'd love suggestions for such. I'm pretty word-oriented myself, so I have a hard time finding effective pictures. I have the ability to host them on a server I run, so where they're from isn't as important as getting links to them.
I mean, my thoughts immediately turn to screenshots of Polygon's excellent and serendipitously named abomination character creation series Monster Factory, but those are all humanoid and maybe not necessarily what you're looking for.

[PhoenixPhyre]

I mean, my thoughts immediately turn to screenshots of Polygon's excellent and serendipitously named abomination character creation series Monster Factory, but those are all humanoid and maybe not necessarily what you're looking for.

I'm not particularly picky. As I said, I'm almost entirely word-oriented, so pictures don't do much for me personally. I do know that they help others. :shrug:

[Unoriginal]

So You Want to Build a Monster


It doesn't have to be a monster...


Joke a side, excellent job! Will probably comment more in-depth once it's finished.

Would you like me to search for pics?

[PhoenixPhyre]

It doesn't have to be a monster...


Joke a side, excellent job! Will probably comment more in-depth once it's finished.

Would you like me to search for pics?

Don't wait until it's "finished." The meat of it is there, at least the parts I'm feeling competent to write. If you have suggestions for the encounter-building parts, go ahead. The templates part will get filled up as I get good suggestions, but that's gonna be slow. All the core stuff is there, the rest are just appendixes.

And yes. Please find pics. I'm bad at that.

I'm willing to make edits as requested--I know I'm quite verbose, for example. Any way I can make this labor of love more useful for others, I'd be happy to.

[Unoriginal]

Something I need to comment on right now, though:

I don't think summoned monsters grant any XP if defeated. Nor do they increase the CR of the creature, unless it's a spell the creature know (in which case the normal rules for spellcasting and CR apply)

Summoned monsters are temporary, and often rely on the caster's Concentration. Monsters that can be beaten by hitting a different monster (the summoner) don't count in the XP budget of the encounter, I'd say.

Also, some pics:

https://img00.deviantart.net/6a06/i/2012/164/9/4/the_dungeon_master_by_ralphhorsley-d53b8cq.jpg

The Dungeon Master, by Ralph Horsley (https://ralphhorsley.deviantart.com/art/The-Dungeon-Master-307893770)

https://78.media.tumblr.com/e0bd5f0862b4bcee3333e004a49b7ab4/tumblr_o4smvhHc5k1v9qvuco1_500.jpg

http://media.wizards.com/2015/images/daily/cardart_ScrolloftheMasters.jpg

http://s3.amazonaws.com/cdn.roosterteeth.com/uploads/images/36737a73-fc05-4ad3-9935-9d5230a1c3c7/original/3122895-1509659684863-rt_profile_pic.jpg

[PhoenixPhyre]

Something I need to comment on right now, though:

I don't think summoned monsters grant any XP if defeated. Nor do they increase the CR of the creature, unless it's a spell the creature know (in which case the normal rules for spellcasting and CR apply)

Summoned monsters are temporary, and often rely on the caster's Concentration. Monsters that can be beaten by hitting a different monster (the summoner) don't count in the XP budget of the encounter, I'd say.

Also, some pics:

Can't see the pics. I waffled on summoning, to be honest. Boosting the CR makes some of the predicted values much closer to the book value, except for devils. I wasn't intending to imply that you award xp for summons, but that being able to summon increases your CR by about the value of the summoned creature's XP.

By RAW, right. It doesn't make a change in CR. But it's in the "variable effect" category in practice for me.

[Unoriginal]

Should see the pics now

[PhoenixPhyre]

Changelog (1/31):

Added a few images (Thanks @Unoriginal!)
Added a set of templates.

What encounter-building ideas/concerns do people want to see addressed?

Terrain, number of creatures, ??

[PhoenixPhyre]

Changelog (2/1):

Added a terrain-based scenario to the Encounter-building part.

Unless there's more interest soon, I'll just let this die.

[Unoriginal]

Hi.

Would you like to try building a monster together so we can do the step-by-step, or...?

Otherwise, I have a few things to write, but it risk to take a short while.

[MrStabby]

I think terrain is important for encounter design, usually less so for monster design.

Exceptions are abilities like a fly/swim speed or earth elemental earth glide ability.

One thing I think is particularly important is sensory perception, more so than covered at present. From darkvision to truesight there is quite some range an they have a big impact on the tools you can use to overcome them. In a similar vein the surprised condition will have a big impact on a party of PCs so stealth ability on predatory monsters can have a really big effect on an encounter.

[PhoenixPhyre]

Hi.

Would you like to try building a monster together so we can do the step-by-step, or...?

Otherwise, I have a few things to write, but it risk to take a short while.

I'd love to do that collaboratively, if someone gives a suggestion and a theme. I'm writing this in between classes, so long bursts come at night or early morning. Anything you want to add would be great.


I think terrain is important for encounter design, usually less so for monster design.

Exceptions are abilities like a fly/swim speed or earth elemental earth glide ability.

One thing I think is particularly important is sensory perception, more so than covered at present. From darkvision to truesight there is quite some range an they have a big impact on the tools you can use to overcome them. In a similar vein the surprised condition will have a big impact on a party of PCs so stealth ability on predatory monsters can have a really big effect on an encounter.

I agree about terrain (hence the positioning of that section in an appendix), although when you're building a monster you also want to know what terrains will help or hinder (what will go well with it).

Vision tends to follow from theme, in my experience. Underground things get darkvision; etc. It doesn't change official CR, but can have a big influence on the design of the encounters.

I tried to mention the stealth/ambush related traits in the traits section--can you look at those and see if anything needs to be added/removed/changed?

[Unoriginal]

I'd love to do that collaboratively, if someone gives a suggestion and a theme. I'm writing this in between classes, so long bursts come at night or early morning. Anything you want to add would be great.

I was thinking of doing a 5e version of the Logokron Devil, formerly from 3.X's Tome of Magic, with the caveat of doing a Bardic devil.

While I think 5e monsters are great, there very few instances in the game's setting that use the Bards' kind of magic, so adding one would be interesting. Furthermore, devils being linked to music is a recurring trope, with works like the Sonata Diabolica, The Devil Went Down to Georgia, Tenacious D's Tribute, etc, not to mention the different style of music said to be influenced by the forces of Hell.

Plus it can illustrate the difference between 3.X monsters and 5e ones.



So, the Logokron is a clever and (for this project) musical Devil who is equal to the Ice Devil in term of power/rank in the hierarchy of the Nine Hell.

[MrStabby]

I'd love to do that collaboratively, if someone gives a suggestion and a theme. I'm writing this in between classes, so long bursts come at night or early morning. Anything you want to add would be great.



I agree about terrain (hence the positioning of that section in an appendix), although when you're building a monster you also want to know what terrains will help or hinder (what will go well with it).

Vision tends to follow from theme, in my experience. Underground things get darkvision; etc. It doesn't change official CR, but can have a big influence on the design of the encounters.

I tried to mention the stealth/ambush related traits in the traits section--can you look at those and see if anything needs to be added/removed/changed?

Some of the ambush stuff is so unpredictable due to complexity of interactions. An ambushing wizard (high initiative ) dropping a fireball might be tougher than expected as the surprised people may not be able to space out. Likewise dropping a wall of force or similar. I think I would be tempted to highlight that when a monster has spells or abilities that do more than damage this can radically change the encounter.

I also think it is worth splitting off abilities that add difficulties depending on the party. Undead are a prime example - tend to be less of a challenge if the party has a number of clerics/paladins.

[PhoenixPhyre]

I was thinking of doing a 5e version of the Logokron Devil, formerly from 3.X's Tome of Magic, with the caveat of doing a Bardic devil.

While I think 5e monsters are great, there very few instances in the game's setting that use the Bards' kind of magic, so adding one would be interesting. Furthermore, devils being linked to music is a recurring trope, with works like the Sonata Diabolica, The Devil Went Down to Georgia, Tenacious D's Tribute, etc, not to mention the different style of music said to be influenced by the forces of Hell.

Plus it can illustrate the difference between 3.X monsters and 5e ones.

So, the Logokron is a clever and (for this project) musical Devil who is equal to the Ice Devil in term of power/rank in the hierarchy of the Nine Hell.

So we're looking at a CR 13-15, spell-caster-equivalent (bardic style) fiend. Are they particularly weaker (physically) than similar devils? Any other key traits? I'm not well versed in 3e monsters, so more guidance would be nice as to the key elements.

I'll start working on that this evening, as I have a long work day today without many breaks.

As to splitting the traits, I may add another color label for those that are strongly party dependent (as opposed to my situational ones which are more about the environment) and adding some discussion

[Unoriginal]

So we're looking at a CR 13-15, spell-caster-equivalent (bardic style) fiend. Are they particularly weaker (physically) than similar devils? Any other key traits? I'm not well versed in 3e monsters, so more guidance would be nice as to the key elements.

I'll start working on that this evening, as I have a long work day today without many breaks.

As to splitting the traits, I may add another color label for those that are strongly party dependent (as opposed to my situational ones which are more about the environment) and adding some discussion

Logokrons weren't weaker than similar devils, and they were covered in magic items, so that they stood a chance against 3.X's typical PCs. We don't have to follow that, though.

On the other hand, two key traits were a longue, tattooed tongue that cursed people who looked at the symbols, and the use of halberds that dealt thunder damage.

I thought we could do the halberd as halberd-guitar hybrids that some of the Logokron would have, like the other Devil weapons.

Also of note, those fellas are Large sized, but slow on their feet (20ft), even if able to fly at 40ft per round.

[PhoenixPhyre]

Logokrons weren't weaker than similar devils, and they were covered in magic items, so that they stood a chance against 3.X's typical PCs. We don't have to follow that, though.

On the other hand, two key traits were a longue, tattooed tongue that cursed people who looked at the symbols, and the use of halberds that dealt thunder damage.

I thought we could do the halberd as halberd-guitar hybrids that some of the Logokron would have, like the other Devil weapons.

Also of note, those fellas are Large sized, but slow on their feet (20ft), even if able to fly at 40ft per round.

Sounds good. So we're at
* Relatively high AC
* Sound/word theme
* Longue (aoe curse)
* long-neck axe (guitar-halberd) (thunder enchant)
* Maybe some word-like/song bard spells or the equivalent.
* slow walking but flying

I'll start working once I have a second to think.

[Unoriginal]

I think it's good to give it the standard devil 18 AC from natural armor.

Not sure if we should keep the flying or not. Could be interesting to not include it. Or include it as a 1/day power.


For the stats, I thought of something like

STR 16

DEX 12

CON 18

INT 19

WIS 16

CHA 20

Also giving them Immunity to Thunder damage.

For melee, the standard devil arsenal of bite + claws when no weapon are available seems fitting.

[PhoenixPhyre]

I think it's good to give it the standard devil 18 AC from natural armor.

Not sure if we should keep the flying or not. Could be interesting to not include it. Or include it as a 1/day power.


For the stats, I thought of something like

STR 16

DEX 12

CON 18

INT 19

WIS 16

CHA 20

Also giving them Immunity to Thunder damage.

For melee, the standard devil arsenal of bite + claws when no weapon are available seems fitting.

Those physical stats look low to me. The Ice devil has 21/14/18.

So something like (shorthand):


Logokron
Large fiend (devil), lawful evil
AC 18 (natural armor)
HP 190 (20d10 + 80) [the average HP at CR 14 is 191]
Speed 20 ft [that's awfully slow]

STR 21 (+5) / DEX 14 (+2) / CON 18 (+4) / INT 19 (+4) / WIS 16 (+3) / CHA 20 (+5)
Resistances: non-magical/silver BPS
Immunity: thunder, fire, poison [the last two come on all major devils]
...
Traits
Devil's Sight
Magic Resistance
Louge (disadvantage on attacks/ability checks if you are looking at it, range 30)
Actions
multiattack: 2 attacks (2x halberd or bite + claws)
Halberd (+ thunder damage)
Bite
Claws

??

[Oramac]

Quick question. I didn't see anything this specific in the Modifying Monsters section.

A little background: When I modify a monster, most of the time I'll lower the AC while simultaneously raising the hit points. The idea being that, for a PC, missing an attack is generally not fun (thus the lower AC), but two-shotting a BBEG is also not fun (thus raising the HP).

Is there a way to calculate how these two things can be changed in relation to each other without changing CR?

For example (and I suck at math so forgive me): An Bulette is CR5, AC17, and 94 average hp.

If I bump it to max HP (9d10+45) that gives it 135 hp. A difference of 41 hp. So according to the 30 hp = +1 CR, now I'm a little over CR6.

So now I need to drop the AC down to get back to CR5. You don't have a specific section on changing AC, but if I'm understanding this right, in order to correct for the +2 dCR of the extra hit points, I need to lower the AC by -2, down to AC15.

So (hopefully) now I'd still have a CR5 Bulette, this time with AC15 and 135 hit points.

Is this right?

[PhoenixPhyre]

Quick question. I didn't see anything this specific in the Modifying Monsters section.

A little background: When I modify a monster, most of the time I'll lower the AC while simultaneously raising the hit points. The idea being that, for a PC, missing an attack is generally not fun (thus the lower AC), but two-shotting a BBEG is also not fun (thus raising the HP).

Is there a way to calculate how these two things can be changed in relation to each other without changing CR?

For example (and I suck at math so forgive me): An Bulette is CR5, AC17, and 94 average hp.

If I bump it to max HP (9d10+45) that gives it 135 hp. A difference of 41 hp. So according to the 30 hp = +1 CR, now I'm a little over CR6.

So now I need to drop the AC down to get back to CR5. You don't have a specific section on changing AC, but if I'm understanding this right, in order to correct for the +2 dCR of the extra hit points, I need to lower the AC by -2, down to AC15.

So (hopefully) now I'd still have a CR5 Bulette, this time with AC15 and 135 hit points.

Is this right?

Every change of 2 AC changes the dCR by 1 (or the overall CR by ~0.5). So upping the health by 40 is an increase of 2 dCR (~15 HP is 1 dCR), so you'd need to drop the AC by 4 to compensate. Be careful though--the reverse is usually the case. AC is on-guidelines, HP is below. In part because the guidelines don't account for advantage/fighting styles/etc very well. Low AC monsters tend to be easier than expected because you're always hitting.

The info is in the "calculating CR" section; I guess I can add a piece to the modifying monsters section...in fact I thought I had. Oops.

[Oramac]

Every change of 2 AC changes the dCR by 1 (or the overall CR by ~0.5). So upping the health by 40 is an increase of 2 dCR (~15 HP is 1 dCR), so you'd need to drop the AC by 4 to compensate. Be careful though--the reverse is usually the case. AC is on-guidelines, HP is below. In part because the guidelines don't account for advantage/fighting styles/etc very well. Low AC monsters tend to be easier than expected because you're always hitting.

The info is in the "calculating CR" section; I guess I can add a piece to the modifying monsters section...in fact I thought I had. Oops.

Hmm. So in that example I'd need to drop it down to AC13. That does seem awful low, even considering the bump in HP.

You make a good point about fighting styles and the like. I suppose it might make more sense to adjust per the calculations (AC13 and 135 hp), then reevaluate based on your specific party makeup.

[Unoriginal]

Those physical stats look low to me. The Ice devil has 21/14/18.

So something like (shorthand):

??

Sounds good, but I'd put the highest phys score in Con.

Also, what do you think of giving it a sonic boom as an attack?

[PhoenixPhyre]

Sounds good, but I'd put the highest phys score in Con.

Also, what do you think of giving it a sonic boom as an attack?

That'll drop the ATK, but sure.

Which do you prefer (wording still sketchy)--

Sonic Dash (recharge 6): The fiend teleports to a position it can see within 60[?] feet. All creatures in a 5-foot-wide line between its starting point and its ending point must make a DC X Constitution saving throw, taking Y thunder damage and being stunned until the end of the fiends next turn on a failed save. Targets take half damage and are not stunned on a success.

[This one makes up for the low speed]
or

Sound Blast (recharge 5-6): All creatures in a 30-foot cone centered on the fiend must make a DC X Constitution saving throw, taking Y thunder damage and being pushed 10 feet on a failed save. On a success, targets take half damage and are not pushed.

[This one gives a PBAoE like a big thunderwave]

Or some combination/something else?

[Unoriginal]

That'll drop the ATK, but sure.

Which do you prefer (wording still sketchy)--

Sonic Dash (recharge 6): The fiend teleports to a position it can see within 60[?] feet. All creatures in a 5-foot-wide line between its starting point and its ending point must make a DC X Constitution saving throw, taking Y thunder damage and being stunned until the end of the fiends next turn on a failed save. Targets take half damage and are not stunned on a success.

[This one makes up for the low speed]
or

Sound Blast (recharge 5-6): All creatures in a 30-foot cone centered on the fiend must make a DC X Constitution saving throw, taking Y thunder damage and being pushed 10 feet on a failed save. On a success, targets take half damage and are not pushed.

[This one gives a PBAoE like a big thunderwave]

Or some combination/something else?

Sound Blast sounds good, but I think it should be 60ft, and only push 5ft.

Shouldn't it be a STR saving throw, if it's to resist getting pushed?

[PhoenixPhyre]

Sound Blast sounds good, but I think it should be 60ft, and only push 5ft.

Shouldn't it be a STR saving throw, if it's to resist getting pushed?

:shrug: For whatever reason I think of thunder as being CON saves, but either works. The numbers were totally spit-balled anyway.

Once I'm home I'll write it up more formally and discuss a bit.

[PhoenixPhyre]

Let's make a monster. This one is targeted at CR 14 and is a sound-themed devil wielding an 'axe'--a guitar-shaped halberd.

First, defense (spoilered for length):



Large fiend (devil), lawful evil
-------------
Armor Class 18 (natural armor)
Hit Points 210 (20d10 + 100)
Speed 20 ft
-------------
STR 18 (+4), DEX 12 (+1), CON 21 (+5), INT 19 (+4), WIS 16 (+3), CHA 20 (+5)
-------------
Saving Throws Dex +6, Con +10, Wis +8, Cha + 10
Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks that aren't silvered
Damage Immunities thunder, fire, poison
Condition Immunities poisoned
Senses blindsight 60 ft, darkvision 120 ft., passive Perception 13
Languages Infernal, telepathy 120 ft.
Challenge 15 (13,000 XP)[calculated below]
------------------
Devil's Sight. Magical darkness doesn't impede the devil's darkvision.
Magic Resistance. The devil has advantage on saving throws against spells and other magical effects.
Louge. The devil's tongue is branded with an arcane symbol that radiates pain to all those that look at it. If a creature starts its turn within 30 feet of the basilisk and the two of them can see each other, the devil can force the creature to make a DC 18 Constitution saving throw if the devil isn't incapacitated. On a failed save, the creature is cursed and suffers disadvantage on all attack rolls and ability checks. At the end of each of its turns the creature can reattempt the saving throw, at disadvantage if it can see the devil, ending the effect on it on a success. A creature that succeeds on this saving throw is immune to the louge of this devil for 24 hours. This effect can also be removed by any spell that can remove curses. All other devils are immune to this effect.
--------------


So far, the Logokron is a slow, lumbering beast. 210 HP is two standard deviations above the average.

Defensive CR:

Effective HP = 210 + 105a = 315
Base DCR = 17
AC for CR 17 = 19
DCR adjustment = (21b - 19)/2 = +1.0
Final DCR = 18


a) the devil gains 50% effective HP from having immunities to many common damage types
b) the devil gains +2 effective AC from magic resistance and 1 from logue (since it's similar to a fear effect.

Now on to offense:



Multiattack. The devil makes two melee attacks with its Thunder Axe.

Thunder Axe. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 15 (2d10 +4 ) slashing damage and 18 (4d8) thunder damage.

Sound Burst (recharge 5-6). All creatures in a 60-ft cone centered on the devil must make a DC 18 Strength saving throw. On a failed save, the target takes 44 (8d10) thunder damage and is pushed back 5 feet. On a success, the target takes half damage.


Those DCs are calculated as DC = 8 + proficiency (+5) + Charisma (+5), and the attack bonus assumes STR + proficiency.

The 3 best rounds are (assuming sound burst doesn't recharge as required):

Sound Burst (affecting 2 targets): 88 damage (2x44)
Two thunder axe hits: 66 damage (2 x (15 + 18))
Two thunder axe hits: 66 damage

For a 3-round DPR of 73.33.

Offensive CR:

Base DPR = 73.33
Base OCR = 11
ATK for CR 11 = 8
OCR adjustment = (9 - 8)/2 = +0.5
Final OCR = 11.5



Final CR = (18 + 11.5)/2 = 14.75, rounding to 15. One higher than planned. If you want to reduce it, I'd drop 2 HD, leaving it at 189 base HP or 283.5 effective HP, for a DCR of 16.5 and a final CR of 14 even.

Tactics:
The logokron is a defensive beast, best suited for area denial. Place it in front of something like a door that must be defended and give it support in the form of quickly-moving devils or those with ranged attacks. It uses its Louge whenever possible and blasts approaching enemies with Sound Burst.

[Jama7301]

To clarify, since my brain is poor at reading comprehension today, this is to be used in conjunction with the "Creating a monster" section of the DMG, instead of as a replacement for it, yeah?

[PhoenixPhyre]

To clarify, since my brain is poor at reading comprehension today, this is to be used in conjunction with the "Creating a monster" section of the DMG, instead of as a replacement for it, yeah?

It's intended to be an alternate take on that section, trying to point out the underlying assumptions and give some different perspectives. Ideally, they'd work together. My numbers pull from that section.

[Jama7301]

Thanks.

I'm terrible at the crunchier side of GMing [I'm much closer to a guy who has grand and fun ideas, but can't drill down into the minutiae and balance well], so when I was seeing all your calculations, part of me felt like you were pulling numbers out of thin air. :smallsmile:

Once I crack open my DMG again, I'll see if I can use this to make a custom monster on here. I'm sure I can find a fun theme to work from, just the numbers will be the hard part.

[PhoenixPhyre]

Thanks.

I'm terrible at the crunchier side of GMing [I'm much closer to a guy who has grand and fun ideas, but can't drill down into the minutiae and balance well], so when I was seeing all your calculations, part of me felt like you were pulling numbers out of thin air. :smallsmile:

Once I crack open my DMG again, I'll see if I can use this to make a custom monster on here. I'm sure I can find a fun theme to work from, just the numbers will be the hard part.

I'm better at the numbers myself. Hope it all helps.

[Jama7301]

Alright, let's see if I made this work.

Jackrunner

CR 1

This tri-pedal mammal has two powerful back legs, and a long front leg it can use to adopt a dasher's stance. The front leg is home to 4 sharp claws that are equally at home digging into dirt or flesh.

Behavior - Jackrunners are typically passive creatures. They subsist primarily on small rodents and grounded birds, as well as berries and vegetation. When provoked, the Jackrunner pod (typically 3-4 adults plus their offspring) will engage in hit and run tactics. Using coordination, they have been known to bring down larger, solitary predators.

Environment: Temperate woods/forest

AC 14
HP 58
Saves - Dex
Prof +2

STR - 13 (+1) DEX - 15 (+2) CON - 11 (0) INT - 7 (-2) WIS - 12 (+1) CHA - 6 (-3)

Claw -+3 vs AC (1d8+1) [5] Slashing

Lunging Headbutt - Reaction - the first time a creature ends its turn adjacent to the Jackrunner in a round, the Jackrunner may use a Reaction to attack the target with a quick, lunging headbutt.

+3 vs AC 1d6+1 [4] Bludgeoning.

Trait - Nimble - On a successful Claw attack, the Jackrunner may Disengage and move 5 feet away from the target of the attack. The Jackrunner may not end it's turn adjacent to the target it hit with the Claw attack.


oCR - 1 for Damage (4.5 + 5.5 = 10) 1 for attack bonus (+2 prof + +1 mod = +3 = CR1 Attack bonus). [1+1]/2 = 1 oCR


dCR calculation I’m a little less sure on. I wanted one more point of AC, and fewer hit points, so I dropped HP down to the upper 50s, and raised the AC by 1. Maybe still hvering around CR 1?



American Football 3-Point Stance (http://www.humankinetics.com/AcuCustom/Sitename/DAM/156/E6411_0828P_0733_ebook1_Main.jpg)

Bunny (http://www.rabbit.org/adoption/bunny.jpg)

General body shape of Kangaroo (https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/RedRoo.JPG/220px-RedRoo.JPG)

[PhoenixPhyre]

I like it.

Checking the numbers--



base dCR: 0.5
AC adjustment: +0.5 (14-13)/2. Traits are null defensively.
Final dCR: 1

As a note, the average HP for a CR 1 creature is 28, with STDEV of 11. 58 is a beefy monster.

Offensive calculations:
DPR (1 claw + 1 headbutt): 10
base oCR: 1
ATK adjustment: 0
Final oCR: 1

The average DPR for a CR 1 creature is 13, with a +4 attack bonus. But since this is a more passive creature, lower offense works.

Final CR: 1

A few notes--it might be better to word the Nimble trait as "when the Jackrunner hits with a claw attack on its turn, it can disengage as a bonus action." The way it's worded, it seems like the creature must retreat if it hits with a claw attack--what if it's penned into a corner? It also runs into the issue of opportunity attacks--does it have to move if it makes a successful OA?

Second--the usual phrasing for the reaction ability is

Reaction:
Lunging Headbutt. When a creature ends its turn within 5 feet of the jackrunner, it can make a headbutt attack against the triggering creature.

No need to specify "the first time on a round"--creatures only get 1 reaction. Also, the headbutt attack goes in the actions section.

Other things to consider: what's the creature's speed? I'd guess more like 40 ft.

[Jama7301]

I knew I was forgetting something. Yeah, speed was 35 feet, but 40 feet makes sense.

I wasn't clear on how to properly do the wording, so thanks for clearing that up.

As for hit points, I was trying to follow the guide in the DMG that listed CR1 HP as 71-85. I felt that was too high, so I wanted to drop it. Knowing that 28 is what it should be, thematically then I'd drop it to 16-21

[PhoenixPhyre]

I knew I was forgetting something. Yeah, speed was 35 feet, but 40 feet makes sense.

I wasn't clear on how to properly do the wording, so thanks for clearing that up.

As for hit points, I was trying to follow the guide in the DMG that listed CR1 HP as 71-85. I felt that was too high, so I wanted to drop it. Knowing that 28 is what it should be, thematically then I'd drop it to 16-21

See the spreadsheet in my sig for the averages. Remember that CR is an average--many creatures have low dCR and high oCR. Also remember that what counts is effective HP--things like resistances/regeneration, etc add to effective health. Thus, lots of creatures have lower HP than you might think, making up for it in defensive traits.

[MrStabby]

Yeah, regeneration is a tough one to gauge the value of. Regeneration on a creature with tough defensive stats - buckets of HP, high armour class can be brutal. The more turns it takes to kill, the more HP it recovers. The same goes for creatures that can disengage.

On the other hand it is weak for creatures of the glass cannon school. If they intend to end combat in a round or two then the extra HP is small.

[PhoenixPhyre]

Yeah, regeneration is a tough one to gauge the value of. Regeneration on a creature with tough defensive stats - buckets of HP, high armour class can be brutal. The more turns it takes to kill, the more HP it recovers. The same goes for creatures that can disengage.

On the other hand it is weak for creatures of the glass cannon school. If they intend to end combat in a round or two then the extra HP is small.

The default round length of combat seems to be 3 rounds. That's why you average over the first 3 rounds of combat for offensive abilities. One offsetting thing is that for big brute monsters, they tend to have higher health pools so +10/round is only a small amount, whereas for the weaker (HP-wise) monsters it may be a significant fraction of their HP pool--the Demilich only has 80 HP (and that's maximized). Compare that to the Tarrasque at 600+ HP. One gets back 1/8th per round with regeneration +10, the other gets back 1/60th.

That's why the effective health method actually works pretty well--regeneration is just $REGEN x $ROUNDS (where CR assumes $ROUNDS == 3).

The big game changer there is troll-like regen (effective even at 0 HP unless you use the weakness)--that turns into a "why won't he die!" moment. I ran a monster like this once--he was a werewolf-demon-thing magically connected to a bunch of sacrificial victims. As long as there were victims "alive", he couldn't die (and wouldn't even go unconscious) and would regain X HP/round. They ended up doing like 300 more damage than his health before they figured out they needed to break the ritual by "killing" the victims to actually kill the sucker.

I use quotes there because the people were already dead but their souls were trapped, so it wasn't murder; more like mercy.

[MrStabby]

I agree (roughly) with the formula of regeneration rate X number of rounds.

I do think that an assumption of #rounds=3 is a big assumption. Flying creatures that can escape, regen then return can drag combat out indefinitely.

I find that this has an impact that really depends on how tough a fight is. A "typical" cr 12 monster for a level 9 party won't be that overpowering but should be a toughish fight. Add modest regeneration to put it to CR 13 and it is likely to overcome the PCs. On the other hand if it is a party of level 11 PCs there is a good chance they won't even know it regenerates before they kill it.

[PhoenixPhyre]

I agree (roughly) with the formula of regeneration rate X number of rounds.

I do think that an assumption of #rounds=3 is a big assumption. Flying creatures that can escape, regen then return can drag combat out indefinitely.

I find that this has an impact that really depends on how tough a fight is. A "typical" cr 12 monster for a level 9 party won't be that overpowering but should be a toughish fight. Add modest regeneration to put it to CR 13 and it is likely to overcome the PCs. On the other hand if it is a party of level 11 PCs there is a good chance they won't even know it regenerates before they kill it.

I generally disfavor hit and run battles (where you don't drop combat between attacks) unless they're wave-style. Lots of "well, you can't do anything, so..." turns spent. If something big enough not to die in 3 rounds runs for long enough to regenerate and comes back, it's going to take enough time that we'd go out of initiative order and those would be separate combats.

In my experience, 3-5 rounds is pretty normal. Note that the HP determination is really assuming that the creature will die 3 rounds after the party starts beating on it on average. In combats with groups of enemies that aren't clumped up, that makes an enemy able to last longer in absolute terms while still dying within 3 rounds of average DPR.

And a CR 13 vs an APL 11 party is an easy fight if solo. In T3, the guidelines are APL +~ 3 for 4 players for a medium solo fight, APL +~ 4 or APL +~ 5 for a hard one. To me, that's working as expected.

[MrStabby]

It die make the guide a bit specific and a lot less useful if it outputs "this is the CR of this creature, but only if your DM style is just like mine and if you don't use this other type of creature".

I think if you are playing vs something like a vampire it SHOULD be smart. It should spider-climb away from fights it is losing to recover HP. Is it a separate encounter when it engages again? Possibly.

What is more interesting is if the vampire is more defensive whilst still engaged? What happens if it climbs away from 75% of the party whilst grappling the other member? A couple of turns whilst the others try to cast fly, find stairs or whatever? The ability to do that really impacts on the fight.

[PhoenixPhyre]

It die make the guide a bit specific and a lot less useful if it outputs "this is the CR of this creature, but only if your DM style is just like mine and if you don't use this other type of creature".

I think if you are playing vs something like a vampire it SHOULD be smart. It should spider-climb away from fights it is losing to recover HP. Is it a separate encounter when it engages again? Possibly.

What is more interesting is if the vampire is more defensive whilst still engaged? What happens if it climbs away from 75% of the party whilst grappling the other member? A couple of turns whilst the others try to cast fly, find stairs or whatever? The ability to do that really impacts on the fight.

That can have an impact, but it's extremely hard to measure. The guide was written from the perspective of the DMG (following those assumptions). I've rarely found that such hit and run tactics are meaningful--usually the monster takes enough damage or is locked down hard and can't make a proper escape, or is unable to successfully grapple and move away in time to avoid getting nuked.

I'll add a note to regeneration about its tactics dependence.