Help with DR on custom monsters.

[p_johnston]

So I have been making some custom monsters for my players to.... enjoy. The problem I've come up with is that three traits I want to give some of my creations aren't covered in the DM's guide and I want advice on how to adjust the monsters accordingly.

So the creatures I'm making are Mage Hunting golems. I want to give them a static ability of immunity to magic below a certain level, the ability to pinpoint mages/magic locations at distance and DR.

1) Golem Immunity (X)- The golem is immune to all magic at or below x levell. Magic items are given a level depending on their rarity. Common=1, uncommon=2, rare=4, very rare=6, legendary=9.
So the thing to note about this is that most golems are straight up immune to magic weapons. This is less of a problem with my group because I'm running a low to no magic campaign but it comes up in a couple of circumstances. I have a blade pact warlock who mostly fights with a summoned weapon, which cannot effect the Golems (he does have a backup spear though).

My Solution- The DM's guide lists magic resistance as equal to +2 ac. I decided to double that to +4 for magic immunity. My figuring is that any boss golem the characters run into will be immune rather resitant to any spells they can cast. Even lower level golems will require either manual dismemberment or annoyingly high level spells to kill. Is this fair?

2)Magic Sense(x)-The creature can sense the presence and location of any caster, magic object, or magic creature in x distance.
This I see as mostly flavor ability. It's like having a really good perception for the purpose of finding magic.

My solution-No adjustment. I figured this one has mostly flavor effect with the slight mechanical advantage that magic users can't sneak up on them. Is this fair?

3)Damage reduction- You know what this is.

My solution- The DM's guide states that regeneration increases the monster effective HP 3 X HP regenerated each turn. I figured DR is more useful as Their will generally by at least two PC's beating a given monster each turn. So I double it to increasing it's effective HP by 6 X DR. Is this fair?

Thanks for any advice. I always worry when doing things like making custom monsters. I don't want to murder my party because I screwed up the how much DR is worth and made the fight to hard. I want to murder my PC's because they were stupid and made mistakes.

[Tenmujiin]

The Rakshasa has immunity to low level magic if I recall correctly. For the DR, the monster creation guidelines basically assume that any given fight will last 3 rounds so take from that what you will. Personally I'd just use resistance to all damage instead.

[p_johnston]

I considered resistance but the main reason I decided against it was that I ended up making up about Eight different types of golems and wanted to differentiate them. I like the idea of the PC's being able to smash the wood golems fairly easily but watching their weapons barely scratch the Steel one.

Thanks for pointing out the Rakshasa. I can probably deconstruct the stat block on that to figure out how they used it to adjust the monster. It's a bit of work but doable.

[Renewal]

I think rather than Spell Immunity affecting AC, it should increase the golem's effective HP, since it's a binary outcome rather than a modification to to-hit bonuses like Magic Resistance is (i.e., Magic Resistance simply decreases a spell's chance of affecting a target, whereas Spell Immunity outright negates it without question unless you use a sufficiently powerful spell).

Here's a breakdown of the rakshasa's Spell Immunity from another site: (http://theangrygm.com/monster-building-201-the-dd-monster-dissection-lab/#comment-24154)


Since [a rakshasa] has magic immunity up to level 6, that means spellcasters level 12 and below can’t touch it. If the spellcasters are doing about half the damage in the party (which is a good estimate below level 12, linear fighters and exponential wizards and all that), that means the Rakshasa’s effective HP should be twice as much if it’s meant to face a party level 12 or below.

Now, for higher level parties, the spellcasters suddenly are able to hit it. Sure, they can only hit it once or twice, but that’s with their most powerful spells. I’d estimate that for higher level parties, the Rakshasa’s effective HP would be increased by a factor of 1.5.

So, effective HP x2 for parties level 12 and under, effective HP x1.5 for parties level 13 and higher.

That’s how I would calculate it anyway. Looking at the DMG, a CR 13 monster should have 251-265 HP. The Rakshasa’s base HP is 110, x1.25 for resistance to nonmagical weapons, then multiply by the weighted average of the magic immunity multiplier (1.8, math math math). That gives effective HP 249.48, pretty damn close to the desired range.

Obviously that’s based on a lot of assumptions, including leaving out the fact that most spellcasters can buff the party or hamper the enemy even without directly affecting them. but that’s how I would think of it.

P.S. Full magic immunity would, in this case give an effective HP multiplier of 2

So we can generalize this analysis to determine a formula that yields an appropriate modifier to effective HP. Taking the rule of thumb from the analysis, full Spell Immunity has an effective HP multiplier of 2, since the average party is generally half-spellcaster and their damage is thus entirely negated. Immunity that a party can bypass with their highest level spells has a multiplier of 1.5, since they can't use cantrips and they'll run out of sufficiently powerful spells a few rounds into combat. This means that our effective HP multiplier will be somewhere between 1.5 and 2 (which ended up being 1.8 in the rakshasa's case). We can simply decide the multiplier by finding an average of our bounds for the multiplier, weighted by the Immunity level, as seen above.

1st level immunity means spellcasters must be at least level 3 to affect the golem; level 2 or below parties are effectively fighting something with full Spell Immunity. So our average is 2*(2/20) + 1.5*(18/20) = 1.55. Since spell levels scale linearly, the modifier increases steadily, giving a neat little chart:

Spell Immunity Level - Effective HP Multiplier
0 (cantrips only) - 1.5
1 - 1.55
2 - 1.6
3 - 1.65
4 - 1.7
5 - 1.75
6 - 1.8
7 - 1.85
8 - 1.9
9 (complete spell immunity) - 2

What do you think?

EDIT: Alternatively, because Spell Immunity is binary, you can simply set the modifier depending on your party's level: if the party's spell levels are below the golem's Immunity, give it an effective HP multiplier of 2, and if they do have spells above the Immunity, give it a multiplier of 1.5. After all, if your party is only level 2 and facing a golem with 1st level Immunity, it doesn't matter that the Immunity can be bypassed at the vast majority of levels: they are still totally boned spell-wise.

Effectively, a golem's Defensive CR will drop as the party levels, simply because its Immunity becomes less of a problem. It is a bit of a messy solution, but that's the nature of the CR system.

[GoodbyeSoberDay]

In general, a "perfect" defense or ability is far better than an equivalent modifier.

There's a reason immunity to lower level magic is only available to PCs as a 6th level spell that requires concentration and an action to cast, and can be dispelled at equivalent spell level. There's a reason why they removed magic immunity from golems, though it makes more sense with mage-killer golems. I'd go with the analysis described above for the Rakshasa, with the caveat that spells do more than just damage.

The detection ability is only "pure flavor" if you're running Combat as Sport (i.e. the players will fight it pretty much straight-up, and they don't think too hard about how they're going to engage it, and they never approach or flee using stealth). Otherwise it's incredibly powerful and should definitely bump the CR. Getting the jump on things is huge in this edition, unless you've altered surprise. That said if your players mostly don't have magic items, and the caster isn't doing much of the sneaking, then I guess it's not huge. It also crucially depends on the range of the ability.

[MrStabby]

So worth considering the whole encounter.

If you have an encounter that is entirely immune to spells the party can cast that is tough. If there is an encounter where only one of many has spell immunity then the casters can focus on the enemies that are vulnerable and the effect is much diminished.

Obviously the impact is also determined by what you tell the players. If they know in advance that the enemy might be immune to an attack so the turn isn't wasted in an ineffective attack then it is easier than if the players are trying to work out what attacks will work.

[Arkhios]

1) Golem Immunity (X)- The golem is immune to all magic at or below x levell. Magic items are given a level depending on their rarity. Common=1, uncommon=2, rare=4, very rare=6, legendary=9.
So the thing to note about this is that most golems are straight up immune to magic weapons. This is less of a problem with my group because I'm running a low to no magic campaign but it comes up in a couple of circumstances. I have a blade pact warlock who mostly fights with a summoned weapon, which cannot effect the Golems (he does have a backup spear though).

My Solution- The DM's guide lists magic resistance as equal to +2 ac. I decided to double that to +4 for magic immunity. My figuring is that any boss golem the characters run into will be immune rather resitant to any spells they can cast. Even lower level golems will require either manual dismemberment or annoyingly high level spells to kill. Is this fair?

As long as you don't increase their actual AC, because that's not the point of a trait being "equal to +X ac". It only serves as a guideline to determine the creature's final challenge rating. Giving them immunity to any and all spells the players decide to cast on the fly seems a little childish move. I would just rather give the golems both resistance to all spell damage and advantage against spell saving throws.



2)Magic Sense(x)-The creature can sense the presence and location of any caster, magic object, or magic creature in x distance.
This I see as mostly flavor ability. It's like having a really good perception for the purpose of finding magic.

My solution-No adjustment. I figured this one has mostly flavor effect with the slight mechanical advantage that magic users can't sneak up on them. Is this fair?

Could be translated to as having the spells Detect Magic(1st-level divination), Arcane Eye(4th-level divination), and True Seeing(6th-level divination) constantly active. You could probably give the golems advantage on checks to determine schools of magic detected, and maybe let them use their reaction instead of their Action for Detect Magic.



3)Damage reduction- You know what this is.

My solution- The DM's guide states that regeneration increases the monster effective HP 3 X HP regenerated each turn. I figured DR is more useful as Their will generally by at least two PC's beating a given monster each turn. So I double it to increasing it's effective HP by 6 X DR. Is this fair?

Again, as long as you don't increase their actual hit points 6 X normal just because they have regeneration. I might give them resistance to X damage and regeneration both (and a vulnerability to Y damage to further differentiate each type of golem.)



Thanks for any advice. I always worry when doing things like making custom monsters. I don't want to murder my party because I screwed up the how much DR is worth and made the fight to hard. I want to murder my PC's because they were stupid and made mistakes.

Well, it's your call. Remember though that if your actions as a DM seem like a personal vendetta against players for being stupid, you might end up having no group at all at a later time. I would much rather have the players pay for their mistakes by having them to survive a hard encounter. Or die trying. At least they would have something to remember either way, instead of just being crushed under DM fiat because "I'm the DM and I say so".

[p_johnston]

Well, it's your call. Remember though that if your actions as a DM seem like a personal vendetta against players for being stupid, you might end up having no group at all at a later time. I would much rather have the players pay for their mistakes by having them to survive a hard encounter. Or die trying. At least they would have something to remember either way, instead of just being crushed under DM fiat because "I'm the DM and I say so".

I actually meant the last part as a joke. I genuinely do worry about killing my players because I screwed up making the monster (hence posting here). That being said I genuinely try my best to play fairly and not kill my players.

I like the advice you gave on the Magic Sensing. I might end up changing over to that so it's actually possible for the group to sneak up on them if they try.

Also I didn't actually increase their HP and AC. Like I said just their effective AC and HP. I know it's for the purpose of Calculating challenge rating only.


Giving them immunity to any and all spells the players decide to cast on the fly seems a little childish move. I would just rather give the golems both resistance to all spell damage and advantage against spell saving throws.

Again I did actually consider doing that. I decided against it for the same reason that I decided on using DR instead of just straight resistance. I like the idea of the more powerful golems being more immune to magic. That way when they have access to high level magic they can just start blasting away the little wood puppets that were so terrifying at lower level. Also I do have golem's ranging form Magic immunity 0-9. So some can be hit by 1st level spells and some can't be damaged at all. The immunity tends to scale with difficulty rating.

I also should have stated that a good 60%-70% of the groups damage is non magic based, and even the heavy magic users can switch over to melee without to much difficulty. When they first encountered them they were able to deal with them pretty easily once they realized they needed to ignore magic and just go with physical damage.

[p_johnston]

The detection ability is only "pure flavor" if you're running Combat as Sport (i.e. the players will fight it pretty much straight-up, and they don't think too hard about how they're going to engage it, and they never approach or flee using stealth). Otherwise it's incredibly powerful and should definitely bump the CR. Getting the jump on things is huge in this edition, unless you've altered surprise.

This does raise a good point. I actually do run the combat as war type of game. The problem is the monster creation section of the DM's guide seems to assume that it's going to be a Combat as Sport type of game. I can't see any traits that change challenge rating based on how hard a monster is to sneak up on. They even straight out state that skills don't change challenge rating. what do you think the ability to not be surprised is worth challenge rating wise?

P.S. The party I'm building these for Includes a Ranger/cleric damage dealer, a warlock tank/crowd control, a druid, and a bard/fighter tank. So no one can sneak up on them currently. It's also worth noting that PC's haven't used surprise rounds very often. The bard can't sneak in his armor, and they try and face any encounter with a full party.

[p_johnston]

Spell Immunity Level - Effective HP Multiplier
0 (cantrips only) - 1.5
1 - 1.55
2 - 1.6
3 - 1.65
4 - 1.7
5 - 1.75
6 - 1.8
7 - 1.85
8 - 1.9
9 (complete spell immunity) - 2


Also thank you so much for the breakdown of the Rakshasa spell immunity. That was pretty much exactly the kind of thing I was looking for. I'll probably switch to that kind of system and just scoot down their health accordingly.

[p_johnston]

So worth considering the whole encounter.

If you have an encounter that is entirely immune to spells the party can cast that is tough. If there is an encounter where only one of many has spell immunity then the casters can focus on the enemies that are vulnerable and the effect is much diminished.

Obviously the impact is also determined by what you tell the players. If they know in advance that the enemy might be immune to an attack so the turn isn't wasted in an ineffective attack then it is easier than if the players are trying to work out what attacks will work.

I actually did consider this. I prepped them with a backstory of an army of golems killing all spellcasters long ago to get them used to the idea. I also have clearly stated that most ruins that exist around the world were ruined during said war. I have currently thrown a few lower level golems at them who they couldn't use magic on to get them used to the idea. I also have an NPC coming up who will be willing to give them more information about golems in general if they ask. I have been dropping clues, even going so far as to tell them they should probably pay closer attention to the write up on the worlds history I gave them.