Shapechanger. The mimic can use its action to polymorph into a disembodied brain or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A Medium or smaller creature adhered to the mimic is also grappled by it (escape DC 15). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an inanimate brain.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

Innate Spellcasting (Psionics). The mimic’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, mind blank (self only)

1/day each: synaptic static, telekinesis

Psychic Grip. A creature grappled by the mimic has disadvantage on Intelligence saving throws.

Pseudopod. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d4 + 4) bludgeoning damage plus 5 (2d4) psychic damage. If the mimic is in object form, the target is subjected to its Adhesive trait and must succeed on a DC 15 Intelligence saving throw or be stunned until this grapple ends.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d4 + 4) piercing damage plus 2 (1d4) acid damage and the target must succeed on a DC 15 Intelligence saving throw or take an additional 5 (2d4) psychic damage.

Melt Brain. Melee Weapon Attack: +7 to hit, reach 5 ft., one incapacitated creature grappled by the mimic. Hit: The target takes 27 (5d10) piercing damage and 27 (5d10) acid damage. If this damage reduces the target to 0 hit points, the mimic kills the target by liquefying and devouring its brain.

Psychic Pulse (Recharge 5-6). The mimic emits a pulse of psychic energy. Each creature within 20 feet of the mimic 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.