Conniving. The mind flayer can take the Disengage or Hide action as a bonus action on each of its turns.

Evasion. If the mind flayer is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the mind flayer instead takes no damage if it succeeds on the save, and only half damage if it fails.

Innate Spellcasting (Psionics). The mind flayer's innate spellcasting ability is Intelligence (spell save DC 16). It can innately cast the following spells, requiring no components:

At will: detect thoughts, disguise self, feather fall, glamour veil (new), levitate
1/day each: dimension door, dominate monster, plane shift (self only), telekinesis

Magic Resistance. The mind flayer has advantage on saving throws against spells and other magical effects.

Sneak Attack (1/Turn). The mind flayer deals an extra 10 (3d6) damage when it hits a target with a weapon attack or an attack using its soulblade and it has advantage on the attack roll, or when the target is within 5 feet of an ally of the mind flayer that isn't incapacitated and the mind flayer doesn't have disadvantage on the attack roll.

Telekinetic Defense. While the mind flayer is wearing no armor and wielding no shield, its AC includes its Intelligence modifier.

Multiattack. The mind flayer makes three soulblade attacks. It can also use its Teleport before or after the attacks.

Soulblade. Melee Spell Attack: +8 to hit, reach 5 ft., one target. Hit: 14 (3d6 + 4) force damage.

Tentacles. Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 15 (2d10 + 4) psychic damage plus 7 (2d6) force damage. If the target is Medium or smaller, it is grappled (escape DC 15) and must succeed on a DC 16 Intelligence save or be stunned until this grapple ends.

Extract Brain. Melee Weapon Attack: +8 to hit, reach 5 ft., one incapacitated humanoid grappled by the mind flayer. Hit: The target takes 55 (10d10) piercing damage plus 10 (3d6) force damage. This damage ignores resistances, and if it reduces the target to 0 hit points, the mind flayer kills the target by extracting and devouring its brain.

Mind Blast (Recharge 5–6). The mind flayer 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 25 (4d8 + 7) 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.

Teleport (Recharge 4–6). The mind flayer teleports to an unoccupied space that it can see within 60 feet of it. Any creatures the mind flayer has grappled are not teleported.