Shapechanger. The mimic can use its action to polymorph into a bullhorn, megaphone, or other sound-amplifying device 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 11). Ability checks made to escape this grapple have disadvantage.

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

Feedback (Object Form Only).  When the mimic casts a spell that deals thunder damage, any creature that fails its saving throw against the spell is deafened until the end of the mimic's next turn.

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

Innate Spellcasting. The mimic's innate spellcasting ability is Charisma (spell save DC 12). The mimic can innately cast the following spells, requiring no material components:

At will: thunderclap, vicious mockery

3/day each: shatter, thunderwave

1/day each: thunder step

Pseudopod. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 1) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 1) piercing damage plus 2 (1d4) acid damage.