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

Innate Spellcasting (Psionics). The mime flayer’s innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:

At will: detect thoughts, levitate

1/day each: dominate monster, plane shift (self only)

Spellcasting. The mime flayer is a 13th-level spellcaster. Its spellcasting ability is Charisma (save DC 15, +7 to hit with spell attacks). The mime flayer has the following bard spells prepared:

Cantrips (at will): dancing lights, friends, minor illusion, vicious mockery

1st level (4 slots): bane, charm person, disguise self, dissonant whispers, hideous laughter

2nd level (3 slots): crown of madness, invisibility, silence

3rd level (3 slots): fear, hypnotic pattern

4th level (3 slots): confusion, hallucinatory terrain

5th level (2 slots): geas, mislead

6th level (1 slot): otto's irresistible dance

7th level (1 slot): forcecage

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

Extract Brain. Melee Weapon Attack: +7 to hit, reach 5 ft., one incapacitated humanoid grappled by the mime flayer. Hit: The target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the mime flayer kills the target by extracting and devouring its brain.

Mind Blast (Recharge 5–6). The mime flayer magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 22 (4d8 + 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.