Great Old One, Cthulhu

Gargantuan aberration (mythic, mythos), chaotic evil

Armor Class 21 (natural armor)
Hit Points 702 (36d20+324)
Speed 40 ft., fly 60 ft., swim 40 ft.

30 (+10) 13 (+1) 29 (+9) 22 (+6) 25 (+7) 30 (+10)

Saving Throws Str +19, Con +18, Int +15, Wis +16, Cha +19
Skills Arcana +15, Perception +16
Damage Immunities cold, poison, psychic
Condition Immunities charmed, frightened, paralyzed, petrified, poisoned
Senses blindsight 60 ft., darkvision 60 ft., truesight 60 ft., passive Perception 26
Languages Deep Speech, telepathy 300 ft.
Challenge 30 (155,000 XP)

Special Traits

  • Innate Spellcasting. Cthulhu’s spell casting ability is Charisma (spell save DC 27). He can innately cast the following spells, requiring no material components:
    • At will: dream, sending, suggestion
    • 3/day: confusion (as a 9th level spell), control weather, feeblemind, weird
    • 1/day: dispel magic, gate, symbol
  • Magic Resistance. Cthulhu has advantage on saving throws against spells and other magical effects.
  • Overwhelming Mind. Cthulhu’s mind is overwhelming in its power and alien structure. He is immune to any effect that would sense his emotions or read his thoughts, and divination spells. This even foils wish spells and spells or effects of similar power used to affect his mind or gain information. The first time a creature other than a fiend or aberration makes mental contact with Cthulhu, it must succeed at a DC 27 Wisdom saving throw or contract indefinite madnessSRD. On a successful save, the creature cannot take reactions and can make either an action or a bonus action (not both) for 1 round; creatures that are immune to being stunned are unaffected. This effect can occur whether Cthulhu initiates mental contact (such as via a dream, or once per round merely by telepathic communication) or another creature attempts to do so (such as via detect thoughts or dominate monster). Once a creature is exposed to Cthulhu’s overwhelming mind, it is immune to this effect for 24 hours.
  • Resurrection. If Cthulhu is killed, his body immediately fades away into a noxious cloud of otherworldly vapor that fills an area out to his reach. This cloud blocks vision as fog cloud but can’t be dispersed by any amount of wind. Any creature in this area must succeed at a DC 26 Constitution save or be poisoned for as long as it remains in the cloud and for an additional 1d10 rounds after it leaves the area. Cthulhu returns to life after 2d6 rounds, manifesting from the cloud and restored to life via true resurrection, but for 2d6 rounds cannot take reactions and can take either an action or a bonus action on his turn but not both. If slain again while he is suffering from this effect, Cthulhu reverts to vapor form again and his essence fades away after 2d6 rounds, returning to his tomb in R�lyeh until he is released again.
  • Starflight. Cthulhu can survive in the void of outer space, and flies through outer space at incredible speeds. Although the exact travel time will vary from one trip to the next, a trip within a solar system normally takes Cthulhu 2d6 hours, and a trip beyond normally takes 2d6 days (or more, at the GM’s discretion).


  • Multiattack. Cthulhu can use his Unspeakable Presence. He then makes six attacks: two with its claws and four with its tentacles. It can shove a creature in place of a claw attack.
  • Claw. Melee Weapon Attack: +19 to hit, reach 40 ft., targets all creatures in a 10-foot square. Hit: 19 (4d6 + 10) slashing damage. Make one attack roll; any creature in the area whose AC is equal to or lower than the result takes damage from the claw.
  • Tentacle. Melee Weapon Attack: +19 to hit, reach 40 ft., one target. Hit: 21 (2d10 + 10) bludgeoning damage. If the target is a creature, it is grappled (escape DC 29). Until this grapple ends, the target is restrained. Cthulhu has four tentacles with which to grapple targets; while a tentacle is being used to grapple, it cannot be used to attack a different target.
  • Unspeakable Presence. Each non-aberration, non-fiend within 300 feet of Cthulhu and aware of him must succeed on a DC 27 Wisdom saving throw or become frightened for 1 minute. A creature that becomes frightened drops to 0 hit points and begins dying. A creature that is immune to being frightened and fails the saving throw becomes incapacitated for 1 minute; at the end of each of the target’s turns it may make a new saving throw, becoming no longer incapacitated on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Cthulu�s Unspeakable Presence for the next 24 hours.


  • Non-Euclidean. Cthulhu does not exist wholly in the physical world, and space and time strain against his presence. He may add a +9 bonus to AC when an attack would hit or +9 to his Dexterity saving throw when he would fail. This can cause an attack to miss or Cthulhu to succeed at a saving throw.

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. Cthulhu regains spent legendary actions at the start of his turn.

  • Detect. Cthulhu makes a Wisdom (Perception) check.
  • Claw Attack. Cthulhu makes a claw attack.
  • Trample (Costs 2 Actions). Cthulhu moves or swims his movement rate without provoking opportunity attacks. He may move through the spaces of other creatures of less than Gargantuan size, ending in an unoccupied space. Each creature whose space he passed through must succeed on a DC 27 Dexterity saving throw or take 19 (2d8 + 10) bludgeoning damage and be knocked prone.


Cthulhu�s lair is typically a grand temple, fallen into obscurity from aeons of neglect. He may also be found keeping court in deep undersea caves. Cthulhu�s dread presence permeates the lair, making it sick with the taint of madness and causing its cyclopean proportions to distort in the mind.

On initiative count 20 (losing all initiative ties), Cthulhu can use one of his lair action options. He can�t do so while incapacitated or otherwise unable to take actions. If surprised, he can�t use one until after his first turn in the combat.

  • Chill. Unnatural chill permeates a 20-foot radius centereed on a point Cthulhu can see within 120 feet. Creatures in the area must succeed on a DC 15 Constitution saving throw or take 14 (4d6) cold damage.
  • Madness. Shadows of the mind afflict a 20-foot radius centereed on a point Cthulhu can see within 120 feet. Creatures in the area must succeed on a DC 15 Wisdom saving throw or suffer a short-term madness.
  • Non-Euclidean Shifts. Cthulhu chooses two creatures within 120 feet that he can see. The targets must succeed on a DC 15 Intelligence saving throw. On a failure, the creature moves up to 10 feet in a direction of Cthulhu�s choice, without provoking opportunity attacks or causing the target to leave a solid surface or a body of water. If both targets fail, Cthulhu can instead switch their positions.

Regional Effects

  • Creatures that sleep within 1 mile of the lair can sense Cthulhu�s dreams. Dreamers may be inspired, frightened, or bewildered.
  • Cthulhu�s huge temples seem to defy ordinary geometry. Passages and rooms may overlap or differ in length, seemingly in contradiction of physical possiblity.
  • Intelligent creatures within 1 mile of the lair may gradually develop various forms of madness. The more sensitive or powerful the intellect, the worse the madness.

These effects end within 1d10 hours of Cthulhu�s final defeat, as he slips into a death that is not death.


Known to some as the Dreamer in the Deep, Great Cthulhu is the mightiest of the Great Old Ones. Cthulhu is represented often in artwork�particularly in sculpture, painting, and poetry, for his influence is particularly strong among such sensitive and creative minds. In these eldritch works of art, he is depicted or described as having a vaguely humanoid frame, but with immense draconic wings and an octopusshaped head. His actual form is somewhat fluid�the Great Old One can shift and reshape his exact countenance as he wills, allowing him to occupy a smaller space than one might expect for a creature that stands over 100 feet tall.

It is fortunate indeed that Cthulhu is currently imprisoned on a distant planet within the sunken city of R’lyeh. There, the Great Old One slumbers away the eons in a state neither quite dead nor living, held in stasis by ancient magic and the potency of the Elder Sign, yet at times the city rises from the sea and the doors to his tomb open, granting Cthulhu limited mobility before he must return to his tomb.

Cthulhu’s Cult. Although Cthulhu is imprisoned on a farflung world, his dreams span the gulfs of existence and are capable of touching upon the sleeping minds of sensitive or artistic souls, inspiring them with insane visions and driving the creation of all manner of eldritch artistry. In such ways, his cult spreads like a night-borne virus of the dreaming mind across all worlds on which sapient life dwells. Cthulhu is worshiped by various aquatic races and folk who dwell along coasts, but also among certain decadent or fringe societies of artists, poets, and philosophers. When they form, his cults are secretive and careful to hide their allegiance to the Great Old One, meeting only in desolate and otherwise abandoned locales hidden from society�s notice. Central among his cult�s beliefs is the prophecy that one day, the stars will be right and Great Cthulhu shall rise from his corpse-city to usher in the end times, wiping clean all worlds to make them ready for his kind. The cultists believe they might be spared this fate through proper obeisance and fealty, when in truth Cthulhu is unlikely to notice the difference between those who worship him and anyone else.

Cthulhu’s cult is associated with cataclysms, dreams, and the stars, and his sacred symbol is a complex rune surrounding an open eye. Cthulhu’s temples are monolithic structures of a stark and cyclopean architectural style, but most of his faithful lack the resources to build such temples and instead make do with what they can, hiding away personal shrines in underground chambers or in shacks or glades in the remote wilderness.

Immortality. Cthulhu does not age, nor does he need to eat or breathe. Only violence can bring about the death of a Great Old One, and even then, only temporarily.

Section 15: Copyright Notice

Mythos Monsters (5E) © 2020, Legendary Games; Authors Michael "solomani" Mifsud, Robert J. Grady, Mark Hart, Jeff Ibach, Alex Riggs, Scott D. Young, Jeff Lee, Matt Kimmel, and Jason Nelson.

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