I would like to make the "last boss" in my Ravenloft Campaign Cthulu, but I'm not familiar with his abilies or possible stats and would like lots of help with designing him. The only think I know currently is that I wish to make him level 29-30. Any help would be greatly appreciated.
i believe someone asked how to convert d20 Call of Clthulhu to 5e. While most people posted how to convert various class/skill/effects, I think I misread the request and wrote guidelines for converting the Old Ones themselves. Among them, Cthulhu, here's the link.
Much appreciated thank you.
I ttok a look at this thread a while ago, this gave the conversions for stats but not the abilities.
The original D20 Call of Cthulhu RPG had a lot of custom spells and abilities for its creatures, that were designed for the 3.5 system, and would need some manual tweaking to work in 5th edition.
Attacks: 6 tentacles +56 melee (4d6+16 dmg, improved critical), 2 claws +50 melee (2d8+8 dmg), stamp +50 melee (4d6+8 dmg)
Face/Reach: 40ft. by 40ft./25 ft.
Special Attacks: Improved Grab, Horrid Constriction 4d6+12, spells
Special Qualities: Divine Qualities, damage reduction 40/+4, divine fast healing 50/round, SR 37, darkvision 60ft., water subtype, fire resistance 25, sonic resistance 25, alter size, alter form.
Spells: All the spells in the Call of Cthulhu book, except for summon/unbind nightgaunt and contact Nodens. In addition to his domain spells and spell-like abilities that all mythos deities posses, he also knows meteor storm, call lightning, circle of death, control weather, firestorm, gate and unhallow. He can cast these 1/day each, as a 40th level sorcerer, without losing sanity.
Horrid Constriction(ex): Once he has a hold of an opponent, each successful grapple check he makes during subsequent rounds automatically deals one of four different effects to the opponent or object grasped: Flesh discorporation (2d4 permanent Str, Dex and Con drain), energy drain (6 negative levels on failed fortitude save DC 39, otherwise only 3 negative levels), madness (sanity and wisdom drop to 1), or desintegration (fortitude save DC 39). Great Cthulhu decided the effect for a given round and for a given tentacle. More than one tentacle may grip one victim.
While I wouldn't normally suggest a Pathfinder to 5e conversion, their Cthulhu might be a better choice than Call of Cthulhu's big C, since their's is built to be fought, not to insta-kill the party (http://www.d20pfsrd.com/bestiary/monster-listings/aberrations/great-old-ones/great-old-one-cthulhu).
frankly, i think they made Cthulhu too weak in d20. When i convert him back i only get a DC 23 for those disintegrate saves. I get more HP than Tiamat, but i think they really gave him shoddy attributes in d20. Lemme see what AD&D gave him..Strength 25, intelligence 20, wisdom 23, dex 20, constitution 25, and charisma negatve 7, which is the same thing as 25 with horror factor. Converting those to 5e, we
get strength 30, intelligence 20, wisdom 26, dex 20, constitution 30, charisma 30.Revising my d20 stat blocks (choosing the better in each case), we have higher strength, dex, con, wis, charisma from AD&D, and higher int from d20. We can assume saving throw effects are based on Charisma because it's a cheap way to say Horror factor = presence = godlike powers, but as a priest, our base bonus is at least +8 from wisdom. Revising it by AD&D standards, the hp and AC went up, which is good. Woops! I almost forgot to fix the Proficiency Bonus! Sorry guys XD
Cthulhu stats in 5e real quick, revised by AD&D Deities & Demigods:
Str: 30 +10, dex:20 +5, con:30 +10, int: 23 +6, wis: 26 +8, cha: 30 +10
he is CR 42,(470,000 XP) which is 12 CR over 30, or 3 steps, so his proficiency bonus is +12.
Saves: str +22, dex +17, con +22, int +18, wis +20, cha +22
Passive Perception = 24+8 +10 = 42
Cthulhu is double proficient in Grappling, like a Rogue is with Acrobatics:
Multi Attacks:Great Cthulhu makes Six attacks with his Tentacles, 2 with his claws (+22 to hit), and a stamp,
which is probably an AOE. Cthulhu is a Siege monster and gets double damage to objects/structures
Legendary resistance, A long list of immunities, including spells lower than 9th level is about right.
(SR 37 meant a 17th level caster would have to roll a natural 20 to bypass, i think, so that means 16th
level and lower magic would fail).
his Tentacles are considered Grappling checks made at: +34
Hit Points: 861 (42d20+420)
AC: 28
Obviously Clthulhu has Legendary Actions, probably stomp and some kind of Psionic AOE
causing insantiy/horror.
Here's two of the 4 possible effects from those 6 tentacle grapples:
Disintegrate: Con save DC 30
Cthulhu Damage has the following note: " necrotic damage, and the target's hit point maximum is
reduced by an amount equal to the necrotic damage taken." Energy drain becomes life drain,
and 6 levels becomes 6 wraith hits (which used to be 1 level per hit), therefore,
Life drain. 106 (24d8+18) necrotic damage. The target must succeed on a DC 30 Constitution
saving throw or its hit point maximum is reduced by an amount equal to the damage taken.
This reduction lasts until the target finishes a long rest. The
target dies if this effect reduces its hit point maximum to 0.
Well, it needs work, but it's beefier now, over 800 hp and capable of way over 600 damage/round. 
A CR42 equivilent is going to be an issue as the players will be around 19-20 when they encounter Cthulhu. he needs to be fought but not too tough otherwise i'll have to introduce some kind of artifact that "nerfs" him enough that he can be fought, thse are the stats i will need
shintashi wrote:
To the OP, start with Tiamat and reskin her to make Cthulhu if you need a CR 30 monster. I would suggest going with a higher HP (800 +/-) and lesser AC (20-22) for Cthulhu and maybe look at the Kraken for types of attaks (withe more damage since the Kraken is only CR 22 or 23). Cthulhu should be doing about 300 dmg/ round per the DMG (but I think this is low for a CR 30 beast IMHO)
FYI, Cthulhu stats in AD&D (Greater God):
Armor Class: -2
Move 18"/36"
Hit Points: 400
# of attacks: 30
Damage/Atack: 1d10 (x30)
Special Attacks: Insanity on failed saving throw on all targets within 100 miles when it is released form its prison
Special Defenses: Immune to magic control, +2 or better weapon to hit, regenerate 10 hit points/ round
Magic Resistance: 80%
Size: L (100' tall)
Alignment: Chaotic Evil
Worshipers Align: Chaotic Evil
Symbol: Image of Cthulhu
Plane: Prime Material Plane
Cleric/Druid: Nil
Fighter: As 16+ HD monster
Magic-User/Illusionist: 20th level magic-user
Thief/Assassin: Nil
Monk/Bard: Nil
Psionic Ability: I
Str: 25 (+7,+14), Int: 20, Wis: 23, Dex: 20, Con: 25, Cha: -7
Mechatarrasque wrote:
But but... if Cthulu awakens, the world just ceases to exist because he's so powerful.
When calculating CR for a legendary monster, there's a vague correlation between hit dice and CR.
Here's some examples:
ancient Black Dragion: 21d20 hp, CR 21
ancient green dragon 22d20 hp, CR 22
tiamat: 30d20 hp, CR 30
it's not a flawless starting point, but it is a starting point. The next thing to factor is in what kind of effects the monster has going on. The CR tables stop at AC 19, that doesn't mean an AC of 25+ has no meaning. Likewise, Proficiency bonuses get factored in, as well as saving throw difficulties. Now, a +12 proficiency bonus is literally in the CR 42 range. That covers column 1. Next, we have AC 28. We have to consult the saving throw table extrapolation to see what that converts to. Above CR 20, +3 CR points = +1 Save DC or AC. So AC 28 is 9 steps over 19, x 3 is 27 steps, plus 20, is step 45-47 on the CR table. DC saves for Cthulhu i have set at either DC 30 flat (Charisma effects) or DC 28 (wisdom effects). The DC 28 would be Step 45-47, while DC 30 would be 6 more steps, i.e., step 51-53.
So column 1: 42, Column 2: 45-47, Column 6: 51-53
The hit point column for 861 is literally the next step after 30, so Column 3 is a meager CR 31, which makes sense if you think of Cthulhu as a classed character rather than a monster, since classed characters get the least amount of CR from hit points. +22 to hit is 9 points higher than +13 at CR 29, and it also has a 3:1 bonus, so 27+29 is 56, so +22 to hit is CR 54-56.
So columns: I: 42, II: 45-47, III: 31, IV: 54-56, V: ?, and VI: 45-47 or 51-53.
That only leaves damage. So far, our average from the 5 is 44+. I currently have damage set at around 700-900, maybe as low as 9 attacks at disintegrate level damage, for an average of 70 (10d6+40 each hit), x 9 equals 630. Either way, that's off the chart again. The damage chart roughly doubles every +8 CR, so 900 hp is roughly 4 times higher than 225 which is CR 25, +8 +8 is CR 41, while 630 damage is roughly double CR 30 damage +8 = CR 38.
Final Tally using lowest values: 42 + 45 + 31 + 54 + 38 + 45, divided by 6 comes to CR 42.5 
shintashi wrote:
If you want him to be over double their CR, why stat him at all? His stuff just works via DM plot magic.
Pathfinder has stats you could use for a conversion.
http://www.d20pfsrd.com/bestiary/monster-listings/aberrations/great-old-ones
http://www.d20pfsrd.com/bestiary/-bestiary-by-challenge-rating/-bestiary-cr-20 has a bunch of +CR20 monsters that are taken from lovecrafts work or are inspired by it.
Here is my attempt at a CR30 Cthulhu:
(please note I have not had time to add spells or verify the CR w/ the DMG. I based this on Tiamat & Tarrasque (CR30) and the Kraken (CR 23?) and a little dragon and mind flayer thrown in.
Cthulhu - DRAFT
Gargantuan abomination chaotic evil
Armor Class 20 (natural armor)
Hit Points 820(40d20+400)
Speed 50 ft., swim 60 ft., fly 50 ft.
STR DEX CON INT WIS CHA
30 (+10) 10(+0) 30(+10) 25(+7) 28(+9) 30(+10)
Savings Throws Str +19, Con +19, Int +16, Wis +18, Cha +19
Skills Arcana +16, Perception +18, Religion +18
Damage Immunities Psychic; poison; bludgeoning, piercing, and slashing from nonmagical weapons
Condition Immunities blinded, charmed, deafened, frightened, paralyzed, petrified, poisoned
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 28
Languages --
Challenge 30 (155,000 XP)
Amphibious. Cthulhu can breathe air and water.
Discorporation. When Clthulhu drops to 0 hit points, it is not destroyed it is simply dispelled (teleported) back to its prison in R’yle and is unable to take action for a time and not until the elder sign is removed from the prison seal.
Cosmic Might. Cthulhu can choose to, on any attack, take a -4 penalty to hit or save DC to gain a +10 damage bonus.
Innate Spellcasting. Cthulhu’s spell casting ability is Charisma (spell save DC 27, +18 to hit with attack spells). Cthulhu can innately cast the following spells, requiring no material components:
At will: ???
3/day each: ???
1/day each: ???
Legendary Resistance (3/Day). If Cthulhu fails a saving throw, it can choose to succeed instead.
Limited Magic Immunity. Unless Cthulhu wishes to be affected,it is immune to spells of 6th level or lower and has advantage on savings throws of all spells and magical effects.
Magic Weapons. Cthulhu’s weapon attacks are magical.
Regeneration. Cthulhu regains 50 hit points at the start of its turn.
Siege Monster. Cthulhu deals double damage to objects and structures.
Actions
Multiattack. Cthulhu can use its Frightful Presence. It then makes either four tentacle attacks or a claw attack.
Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 65 (10d10 + 10) piercing damage If the target is a large or smaller creature grappled by Cthulhu, that creature is also swallowed, and the grapple ends. While swallowed, the creature I blinded and restrained, it has total cover against attacks and effects outside Cthulhu, and it takes 65 (10d12) acid damage at the start of each of Cthulhu’s turns.
If Cthulhu takes 60 damage or more on a single turn from a creature inside it, Cthulhu must succeed on a DC 25 constitution saving throw at the end of its turn or regurgitate all swallowed creatures in a space within 15 feet of Cthulhu. If Cthulhu is reduced to 0 hit points all swallowed creatures are no longer restrained and appear, prone, in the space formerly occupied by Cthulhu (refer to discorporation)
Claw. Melee Weapon Attack: +16 to hit, reach 25 ft., one target.
Hit: 46 (8d8 + 10) slashing and bludgeoning damage and the target is grappled (escape DC 27). Until the grapple ends the target is restrained. Cthulhu can grapple up to 2 large or smaller targets with its claws.
Tentacle. Melee Weapon Attack: +19 to hit, reach 75 ft., one target. Hit: 28 (4d8 + 10) bludgeoning damage and the target is grappled (escape DC 24). Until the grapple ends the target is restrained. Cthulhu can grapple up to 10 large or smaller targets with its tentacles.
Fling. One huge or smaller object held or grappled by Cthulhu is thrown up to 200 ft in a direction of its choosing and knocked prone. If a thrown target strikes a solid surface the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 19 Dexterity saving throw or take the same damage and be knocked prone.
Frightful Presence. Each creature within 1000 feet of Cthulhu must succeed on a DC 24 Wisdom saving throw or become frightened for 3 days. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the Chtulhu’s Frightful Presence for the next 24 hours. For each day a creature is under the influence of Cthulhu’s frightful presence it loses one level of exhaustion.
Psychic Blast (Recharge 5-6). Cthulhu emits a wave of psychic energy in a 500-foot radius. Each creature in that area must succeed on a DC 27 Charisma saving throw or take 49 (6d12+10) psychic damage and be stunned for 5 minutes, taking half damage on a successful save. A stunned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Legendary Actions
Cthulhu can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. If Cthulhu has unspent legendary actions at the end of the round, it may spend and immediately use its remaining legendary actions. Cthulhu regains spent legendary actions at the start of its turn.
Move. Cthulhu can move half her speed.
Regenerate. Cthulhu regenerates 50 hit points
Attack. Cthulhu makes a two tentacle attacks or one claw attack.
Grappled (Costs 2 Actions). Cthulhu can make a bite or fling attack on a grappled target.
Teleport (Costs 2 Actions). Cthulhu can innately cast the teleport spell.
Recharge (Costs 3 Actions). Cthulhu recharges psychic blast.
dave that's a pretty good CR 30 Cthulhu, actually. You have a lot of material about Lovecraft and Cthulhu, and you said you wanted Tiamat to be higher than CR 30, if i recall. What in your opinion is Cthulhu? Do you think Cthulhu should be weaker than, or comparable to Tiamat? And are you aware that the vast majority of people everywhere familiar with the mythos would expect Cthulhu to 1-round a CR 30 monster, even without knowing anything about CR or combat rounds?
Jimjams, when you say level 29-30, do you mean you want an adventuring party of level 29-30, or do you mean you want Cthulhu as weak as a tarrasque? I had a ranger thief punk a Tarrasque so badly the DM actually slammed the book shut and gave up in round 11, exactly 7 days ago. How do you want things to go down? Do you want your Ravenloft characters to win? What level are they supposed to be when they run into the final boss?
IMHO, here's how a fight between Tiamat and Cthulhu would go.
Round Zero: Cthulhu exists in the same spacetime continuum as Tiamat.
Round One: Cthulhu scrambles Tiamat's capacity to process which orifice is which
When Tiamat attempts to use breath weapons, they begin defacating and puking all
over themselves. Massive heads slam into each other as control of the number of
limbs and heads becomes confused and precarious. Schizophrenia breaks out
between the heads as the red and white heads try to eat each other.
Cthulhu transforms Tiamat into something so horrible i can't even post it because
it isn't suitable for children.
round Two: Cthulhu uses their new horrible unspeakable thing that used to be
tiamat as a thrall, to destroy the world.
round Three: The Outer Gods return and Existence as we know it ends.
... what? were you expecting me to roll some epic dice and talk about attacks and armor class, or use my 3/day legendary abilities?
shintashi wrote:
shintashi wrote:
shintashi wrote:
Dave, I appreciate your honesty. Fan boy fallacies are notorious for stat write ups, and I'm quite sure every RPG has a dozen or more examples in every volume. In my case, I have no particular fondness for the Lovecraft mythos any more than the D&D version of Tiamat. A person who has so much bias toward one of the existing CR 30 monsters should probably not be used as a reference for calculating statistics for creatures that may pose an objective threat to that perceived awesomeness.
Then again, the problem between the mythology of Tiamat and the mythology of Cthulhu is perceptual levels of metaphor and ignorance. Tiamat was envisioned at a time where eyes or tears could become rivers, where a club could smash the skull holding these eyes, and where the tail of the self same creature becomes the milkyway. It's fanciful, but also ridiculous, and based on perception with no understanding of things like distance or mass or what actually is out there in heavens. Basically, a badly drawn cartoon, possibly with crayons, of the sun, moon, and stars, all neatly fitting on to a piece of paper, or in the case of ancients, cave paintings, stone walls, and scrolls.
Cthulhu is from a completely different set of mythological structures. He stands wading through the ocean not because it is what the author wants to depict with a crayon, but because he is literally hundreds of meters tall and can change his size at will, oddly changing his mass as well. When he steps on someone, they tend to be pasted regardless of how courageous they are or whatever funny poems are written about them, because with Cthulhu, it isn't a popularity contest by drunken Sumerians or Babylonians. Cthulhu exists in a world of weights and measures, of distances, stellar masses and aeons. Therefore, while Tiamat is a whimsical character of fancy, Cthulhu is really just a cosmic alien dimensional horror, like something from Event Horizon, but worse.
D&D ran into this problem several times with different pantheons. Some got stronger, some got weaker. When a guy is said to drink a third of the ocean, the stat writers have to decide "is that drunken nonsense, or did the deity actually drink several million cubic miles of water?"
D&D spends a lot of time dancing between fantasy figures and abstractions and a few physical engines. But if Belief is the thing, sadly, the popularity of Cthulhu has consumed Tiamat in the 21st century. As popularity contests go, I don't think Tiamat could win that contest. Millions of people around the world believe Cthulhu to be sickly badass and wrong, and what most of them who know of Tiamat think, amounts to another Turtle god or pile of hp waiting to award XP upon death. That's a cultural division that basically means, objectively, it would be prudent to award Cthulhu attributes higher than whatever Tiamat is said to have.
shintashi wrote:
Cthulu is an uncaring horror from a literary world where the author of the tales regularly falls unconscious because he sees something spooky, and he has so far failed to destroy the world.
Tiamat is a purposed evil diety from a world of swords and sorcery full of badasses, who has also failed to destroy the world.
Given the calibur of their opposition, I'm inclined to say that Tiamat would have to be the scarier foe.
Also no writeup of Cthulu is complete without his "eats 1d4 PCs per round" ability.
Saeviomagy wrote:
WOW, you guys just blow me away! Thank you so much for all your imput, I will take what each of you have said and use it when building Cthulhu for my campaign boss.
dave2008 wrote:
Jimjams wrote:
Imaculata wrote:
Imaculata wrote:
dave2008 wrote:
The whole point of me wanting a Cthulhu "old one" as my endboss is becuase it fits with the Ravenloft theme of Horror/madness well. I'm not looking for a H.P lovecraft specific monster, more a giant monster that inflicts madness, and Cthulhu seemed to fit that description better. I understand both the worlds or D&D and Call of Cthulu have major differences, I merely think I'm paying Lovecraft homage in this way.
The last stage of my campaign includes Ithilids and Elder(God) brain that the PC's have to defeat, well, the god brain will survive and decide it is dont with this realm and "adventures" coming to kill it so it decides it's efforts will be directed in breaking Cthulhu out from it's prison to annhilate the Ravenloft world. The Pc's will slowly discover this over the next few levels peicing together the reason for the inceased incidents of madness and the diminishing barriers of the domains.
The final confrontation will see the PC's and several Doman Lords such as Azalin, Strahd and others banding together to fight off the common enemy, legions of undead, demons and lycanthropes against the hords of the star realm such as Illithids, intellect devourers, slaads and so forth...
Most of the battle will be done through narration while the PC's main job is to confront Cthulhu himself.
i really think this will be a great end to the groups efforts, I really want to represent Cthulhu well, as i'm not very familar with the ethos.
Thank you all for your efforts, please feel free to give suggestions on my story arc idea as would love to do more for my players.
Imaculata wrote:
I think I read somewhere that when Thor fights the Hulk, if it is in the Hulk's comic book, the Hulk will win, and if it is in Thor's comic book, Thor will win. For better or worse, D&D is Tiamat's comic book.
Mechatarrasque wrote:
shintashi wrote:
Jimjams wrote:
Mechatarrasque wrote:
shintashi wrote:
dave2008 wrote: