Legendary Resistance (5/day). If C'thun fails a saving throw, it can choose to succeed instead.
Summon Tentacles. C'thun starts combat with five Claw Tentacles, and five Eye Tentacles. Each time it starts its turn, roll 1d8 for each type of tentacle. The number rolled is the number of that tentacle type that is summoned from the ground. Each tentacle appears on a random space (see stat block for tentacles), and cannot appear in the same space as another tentacle. Any creature standing in an area where a tentacle appears is affected by the tentacle's Ground Rupture trait. Every ten tentacles that are destroyed summons a large variant. Flip a coin to determine whether it is a Claw or Eye type.
Feeder Tentacle. At the start if each of it's turns, and if there is no Feeder Tentacle currently active, C'thun summons a Feeder Tentacle. Only one of these tentacles can exist at a time. The tentacle appears on a random space (see tentacle stat block), and cannot appear in the same space as another tentacle. Any creature standing in an area where a tentacle appears is affected by the tentacle's Ground Rupture trait.
Limited Magical Resistance. Unless it wishes to be affected, C'thun is immune to spells of 5th level or lower. It has advantage on saving throws against all other spells and magical effects.
Regeneration. C'thun regains 20 hit points at the start of its turn.
Deep Roots. C'thun cannot be affected by the Banishment spell or any other similar effect.
Multiattack. C'thun can use it's Frightful Prescence. It then attacks with each of its Claw Tentacles or each of its Eye Tentacles or uses it's Feeder Tentacle and then Consume.
Claw Tentacles. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 7 (2d6) bludgeoning damage or 21 (6d6) bludgeoning damage if it is the large variant.
Eye Tentacles. Ranged Weapon Attack: +18 to hit, range 300 ft., one target. Hit: 7 (2d6) force damage or 21 (6d6) force damage if it is the large variant.
Feeder Tentacle. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 7 (2d6). On a hit the target is grappled.
Consume. C'thun attempts to swallow one Large or smaller creature it is grappling. A grappled creature must succeed on a DC 22 Strength saving through or be swallowed. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside C'thun, and it takes 42 (12d6) acid damage at the start of each of C'thun's turns.
If C'thun takes 50 damage or more on a single turn from a creature inside it, C'thun must regurgitate all swallowed creatures, which fall prone in a space within 10 feet of C'thun. If C'thun dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.
Eye Ray. C'thun uses both of the following magical eye rays:
1. Force Chain Ray. The targeted creature must succeed on a DC 24 Dexterity saving throw, taking 55 (10d10) force damage on a failed save, or half as much damage on a successful one. When this effect hits any target, each creature within 20 feet must also make the saving throw. Each time the effect jumps to a new target the damage is increased by 27 (5d10) force damage.
2. Death Ray. The targeted creature must succeed on a DC 26 Constitution saving throw, taking 78 (12d12) necrotic damage on a failed save. The target dies if the ray reduces it to 0 hit points.
Frightful Presence. Each creature of C'thun's choice that is within 240 feet of C'thun and aware of its must succeed on a DC 26 Wisdom saving throw or become frightened for 1 minute. 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 C'thun's Frightful Presence for the next 24 hours.
C'thun can take 5 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. C'thun regains spent legendary actions at the start of its turn.
Detect. C'thun makes a Wisdom (Perception) check.
Move. C'thun moves up to it's speed.
Tentacle Attack (Costs 2 Actions). C'thun attacks with all of its Claw Tentacles or all of it Eye Tentacles.
Eye Ray (Costs 3 Actions). C'thun uses either its Force Chain Ray or Death Ray.
Summon Tentacles (Costs 5 Actions). C'thun uses it's Summon Tentacles trait.
Description
C'thun's form is incomprehensible to any mortal. It is said that if any creature were to be unfortunate enough to gaze upon its full form, they would descend into an inescapable madness. From what has been seen of it's body, beings have described countless tentacles, and a single, lidless, omnipotent eye.
Countless millennia ago C'thun came into being from unknown origins and rooted itself deep in the earth itself. From its being, C'thun spawned insectoid like creatures to serve as its slaves. With the help of its slave children, C'thun's kingdom grew larger and larger, eventually spanning over half a continent. Its newly named Black Empire sought to enslave elementals from the higher planes.
After an unknowable amount of time, the Gods that blinked into existence saw the taint that C'thun's empire had spread and knew what had to be done. After waging war with the Black Empire for eons it was clear that C'thun could not be uprooted, but it could be imprisoned. With all the might that the Gods could muster, they forged a prison that could contain the evil abomination. To ensure that C'thun's imprisonment would be permanent, they created jailers to oversee the prison and ensure that it remained untouched by mortals and Gods alike for the rest of eternity.
But even the Gods aren't eternal, and many came and went, all the while C'thun sat in its prison, waiting. Now, not even the Gods can recall that this ancient evil exists. C'thun spent its eons in captivity slowly building its army, and working to corrupt the minds of its jailers.
Holes and cracks have begun to form in the cell that holds C'thun and its children have begun to spill forth and ravage the land. Unless it is stopped, the world may yet see the second rise of the Black Empire.
Lair and Lair Actions
Lair Actions
On initiative count 20 (losing initiative ties), C'thun takes a lair action to cause one of the following effects; C'thun can’t use the same effect two rounds in a row:
- Sand pours in from the ceiling above obscuring the area until the end of the round. Any creature that targets C'thun with an attack does so with disadvantage.
- A sinkhole with a five foot radius opens up beneath three creatures. Each creature must make a DC 15 Dexterity saving throw, or sink into the ground up to their waist. A creature that sinks into the ground is restrained, and must make succeed on a DC 14 Strength saving throw to free themselves. Each area affected by this becomes difficult terrain.
- An inky black circle with a 20 foot radius appears on a point C'thun can see within range. Each creature within the area of effect must succeed on a DC 16 Wisdom saving throw. On a failed save a creature takes 36 (8d8) psychic damage and the creature can't take any actions until it leaves the affected area.
Regional Effects
The region containing C'thun’s lair is corrupted by the ancient magic it emits, which creates one or more of the following effects:
- Water within 3 miles of the lair evaporate in minutes.
- Sinkholes in the sand open and close seemingly at random, swallowing up negligent adventurers.
- Spending more than a few hours within 5 miles of the lair causes any creature to begin hearing indiscernible whispers. If a creature tries to understand the whispers there is a 25 percent chance that they gain one effect from the short-term madness table in the DMG.
If C'thun dies, these effects fade over the course of 1d20 days.
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