Large aberration (mindflayer becoming ulitharid), lawful evil
Armor Class: 15 (breastplate)
Hit Points: 99
STR DEX CON INT WIS CHA
13( + 1) 12 ( + 1) 13 ( + 1) 20 ( + 5) 18 ( + 4) 18 ( + 4)
Skills: Arcana +8, Deception +7, Insight +8, Perception +8, Persuasion +7, Stealth +4
Senses: passive Perception 17
Languages: Deep Speech, Undercommon, telepathy 120 ft.
Challenge: 8 (3,900 XP)
Magic Resistance. C’thall has advantage on saving throws against spells and other magical effects.
Innate Spellcasting (Psionics). C’thall’s innate spellcasting ability is its Intelligence (spell save DC 16). It can innately cast the following spells, requiring no components:
At will: detect thoughts, levitate
1/day each: confusion, dominate monster, plane shift (self only), project image, telekinesis
Tentacles. Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 21 (3d10 + 4) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 14) and must succeed on a DC 16 Intelligence saving throw or be stunned until this grapple ends.
Extract Brain. Melee Weapon Attack: +8 to hit, reach 5 ft., one incapacitated humanoid grappled by C’thall. Hit: The target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, C’thall kills the target by extracting and devouring its brain.
Mind Blast (Recharge 5-6). C’thall magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 16 Intelligence saving throw or take 26 (4d10 + 4) psychic damage and be stunned 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.
At initiative roll 20 (losing initiative ties), C’thall can take a lair action to cause one of the following effects; C’thall can’t use the same effect two rounds in a row:
Psionic Intuition. C’thall taps into the psionic power of the brain-hive to sense his enemies’ plans. Until initiative count 20 on the next round, enemies have disadvantage on all attack rolls or ability checks made against him, and C’thall has advantage on all saving throws.
Brainbirthing. C’thall calls forth Intellect Devourers by feeding the brain-hive psionic energy leached from enemies inside the lair. Each enemy within the lair must make a successful Intelligence saving throw (DC 16) or take 1d4 psychic damage. For each enemy that fails, an Intellect Devourer with 1 hit point emerges from the brain-hive and is next in initiative order.
Nautiloid Engine. C’thall activates the psionic engine of the nautiloid, if it hasn’t been disabled, to do one of the following:
Psychic Barriers: The barriers around the ship are activated. Any creature besides C’thall or the Intellect Devourers that attempts to enter the ship must first make a successful Intelligence saving throw (DC 16) or take 5d10 psychic damage.
Psychic Regeneration: If C’thall is within the ship, he harnesses the energy of the psionic engine to heal his wounds and regain 4d8 hit points.