I desperately need help on calculating a CR for an Ogre Mage Ghost!

[Arkhios]

Inspired by another thread (http://www.giantitp.com/forums/showthread.php?497231-5th-Edition-Homebrew-magic-item-Glaive-of-the-Ogre-Magi) after "sleeping on the idea", I decided to make an undead version of an Ogre Mage (Oni), in this case a Ghost. What I did was I more or less added Ghost's abilities on top of an Oni's statblock, with very minimal changes. The current Challenge Rating (10) is handwaved, but I'd like to know an exact one.

I find it's rather complicated creature to calculate and I'm not the most experienced with that. Which is why I turn to you, fellow playgrounders. I've made a thread on Homebrew forum (http://www.giantitp.com/forums/showsinglepost.php?p=20534771&postcount=1) ages ago, and just updated the first post about it, but it seems that the 5e/Next sub-forum is way more actively read.

What I'd especially want to know is that if a monster has multiple abilities that increase and/or double the effective hit points, am I supposed to add them all together, once per increase type, or just once, the biggest increase relevant?

Help would be appreciated! Thanks in advance :)

[BurgerBeast]

I get CR 13. It's hard without having the casting level (I assumed he casts level 5 spells, which is the spell level of cone of cold). I'll walk you through how I do it, which is not necessarily right, but at least you can see my thinking and then decide.

Start with the base numbers:

AC 16 hp 110 -> DCR 4
Att +7 Dmg 48 -> OCR 7
The most damaging combo I figure is to cast Cone of Cold (44 damage) followed by Sleep (13d8 for 71 damage) followed by Multiattack with the glaive (30 damage). This averages 48 damage per round.

Next thing to consider is Fly, which basically grants +2 to AC if the creature can fly and attack at range. I don't personally think this should be applied because of the ghost's limited ranged ability.

Next consider the rest of the abilities. Rather than use multipliers, I like to convert to a flat bonus. If the monster has 110 hp, then x1.5 adds 55 hp, and x2 adds 110 hp. Using this as a guideline, we get:
Immunities +55
Resistances +27
Regeneration +30
Horrifying Visage +27
Possession +110
TOTAL +249

So the final adjusted values are:

AC 16 hp 359 -> DCR 19
Att +7 Dmg 48 -> OCR 7

Final CR = 13

[Arkhios]

I get CR 13. It's hard without having the casting level (I assumed he casts level 5 spells, which is the spell level of cone of cold). I'll walk you through how I do it, which is not necessarily right, but at least you can see my thinking and then decide.

Start with the base numbers:

AC 16 hp 110 -> DCR 4
Att +7 Dmg 48 -> OCR 7
The most damaging combo I figure is to cast Cone of Cold (44 damage) followed by Sleep (13d8 for 71 damage) followed by Multiattack with the glaive (30 damage). This averages 48 damage per round.

Next thing to consider is Fly, which basically grants +2 to AC if the creature can fly and attack at range. I don't personally think this should be applied because of the ghost's limited ranged ability.

Next consider the rest of the abilities. Rather than use multipliers, I like to convert to a flat bonus. If the monster has 110 hp, then x1.5 adds 55 hp, and x2 adds 110 hp. Using this as a guideline, we get:
Immunities +55
Resistances +27
Regeneration +30
Horrifying Visage +27
Possession +110
TOTAL +249

So the final adjusted values are:

AC 16 hp 359 -> DCR 19
Att +7 Dmg 48 -> OCR 7

Final CR = 13

Thanks! I just made my own calculations, but I'm not sure if I got it right, ending up with as high as CR 14. I may have stumbled upon unnecessary details multiple times, so I'm embarrased to list my math here. I'm fairly positive that your method is pretty viable indeed.

Edit: yes, I think that an Ogre Mage would cast up to 5th level spells, although none of them at higher than their minimum levels, because Innate Spellcasting =/= Spellcasting. If I understood it correctly, Innate Spellcasting is similar to Spell-Like Ability, meaning that while they can cast a 5th level cone of cold (only once per day!), it's only for that one spell.

Although I have to wonder, how did you come up with 44 damage from a minimum of 8d8 spell? Average for that would be 36. And the sleep, if it truly were a 5th level version of it, would be only ~59, while at 1st level it's only ~23. (a d8 averages at 4.5)

[BurgerBeast]

Sorry for the late reply.


Thanks! I just made my own calculations, but I'm not sure if I got it right, ending up with as high as CR 14. I may have stumbled upon unnecessary details multiple times, so I'm embarrased to list my math here. I'm fairly positive that your method is pretty viable indeed.

It's like that with CR. I once made a thread because I calculate the CR for a monster on the assumption it would be one CR, and then on the assumption it would be one higher, and it caused the resulting CRs to flip places. Something like: Assume 4 -> Calculate 5. Assume 5 -> Calculate 4. It's just weird.


Edit: yes, I think that an Ogre Mage would cast up to 5th level spells, although none of them at higher than their minimum levels, because Innate Spellcasting =/= Spellcasting. If I understood it correctly, Innate Spellcasting is similar to Spell-Like Ability, meaning that while they can cast a 5th level cone of cold (only once per day!), it's only for that one spell.

Sounds good.


Although I have to wonder, how did you come up with 44 damage from a minimum of 8d8 spell? Average for that would be 36. And the sleep, if it truly were a 5th level version of it, would be only ~59, while at 1st level it's only ~23. (a d8 averages at 4.5)

I'm an idiot. I used 5.5 instead of 4.5 as the average roll. I'd like to blame lack of sleep, but no, I'm just an idiot.

[Arkhios]

Sorry for the late reply.

It's like that with CR. I once made a thread because I calculate the CR for a monster on the assumption it would be one CR, and then on the assumption it would be one higher, and it caused the resulting CRs to flip places. Something like: Assume 4 -> Calculate 5. Assume 5 -> Calculate 4. It's just weird.

I'm an idiot. I used 5.5 instead of 4.5 as the average roll. I'd like to blame lack of sleep, but no, I'm just an idiot.

Oh, it's alright, accidents happen :D In this light it would seem that while a Sleep spell would indeed classify as a "damage" spell, the most effective 3 rounds would be: Cone of cold (36) + Multiattack (30) + Multiattack (30), averaging nicely to a solid 32 points, therefore dropping its OCR to 4 instead of 7. Whoops! :D

Referring to your previous calculations I get a total CR of 12.

AC 16, HP 359 = DCR 19
att +7, dmg 32 = OCR 4+1 (att is 2 points higher than the damage would suggest -> CR +1)

Overall, I found that this buddy is "a bit" too high for when I intended my group to face it. Might have to weaken it somehow to get closer to assumed CR of a 4 or 5. (Although, I might still use the higher CR monstrosity at a later point!). Maybe if I used the Ghost's stats as a basis, and just added the Ogre Mage abilities in (instead of other way around, like previosly)...

Edit:

Actually, I ended up making one quite simple, yet massive change to the original build; changing its size from large to medium, which ended up affecting their multiattack damage potential quite a bit, and along with lesser hit points, it decreased the CR all the way down to 10, if my calculations are correct (CR 10 is actually what I had imagined for them in the first place).

Anyway, here's the "lesser" version based upon Ghost with abilities from Ogre Mage. I did the calculations with the method Burgerbeast used, but for reference you may do your own calculations if you wish:

medium undead, lawful evil
Armor Class 14 (ghost ring mail)
Hit Points 45 (10d8 + 0)
Speed 0 ft., fly 30 ft.
STR 17 (+3), DEX 11 (+0), CON 10 (+3), INT 14 (+2), WIS 12 (+1), CHA 17 (+3)
Skills Arcana +4, Deception +5, Perception +3
Damage Resistances acid, fire, lightning, thunder; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities cold, necrotic, poison
Condition Immunities charmed, exhaustion, frightened, grappled, paralyzed, petrified, poisoned, prone, restrained
Senses darkvision 60 ft., passive Perception 13
Languages Common, Giant
Challenge 5 (1800 XP)
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Ethereal Sight. The ogre mage ghost can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.
Incorporeal Movement. The ogre mage ghost can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Innate Spellcasting. The ogre mage ghost's innate spellcasting ability is Charisma (spell save DC 13). The oni can innately cast the following spells, requiring no material components:
At will: darkness, invisibility
1/day each: charm person, cone of cold (avg Dmg 36), gaseous form, sleep (avg hp 22)
Magic Weapons. The ogre mage ghost's weapon attacks are magical.
Regeneration. The ogre mage ghost regains 5 hit points at the start of its turn if it has at least 1 hit point.
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ACTIONS
Etherealness. The ogre mage ghost enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.
Horrifying Visage. Each non-undead creature within 60 feet of the ghost that can see it must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d4 x 10 years. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this ghost's Horrifying Visage for the next 24 hours. The aging effect can be reversed with a greater restoration spell, but only within 24 hours of it occurring.
Ghost Touched Glaive. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 8 (1d10 + 3) slashing damage and 7 (2d6) necrotic damage.
Possession (Recharge 6). One humanoid that the ghost can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the ogre mage ghost; the ghost then disappears, and the target is incapacitated and loses control of its body. The ghost now controls the body but doesn't deprive the target of awareness. The ghost can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies. The possession lasts until the body drops to 0 hit points, the ghost ends it as a bonus action, or the ghost is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the ghost reappears in an unoccupied space within 5 feet of the body. The target is immune to this ghost's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

The ghost is the soul of a once-living Ogre Mage, bound to haunt an object from its life, in this case, its Glaive. As soon as a person touches with the Glaive, the person is subject to Possession.