Chester The Chest

Shapechanger. The mimic can use its action to polymorph into an object 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 Huge or smaller creature adhered to the mimic is also grappled by it (escape DC 17). 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.

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

The Underdark trader. Chester is unlike most mimics he has sentience. He is prone to talking and trading. Chester has two items from magic item table G (DMG p144) that he will trade for other magic items. He also will not hesitate to use his magic items in combat. After Chester dies his magic items have a 80% change to be destroyed.

Multiaction. Chester makes 2 Pseudopod attacks and 1 bite attack.

Pseudopod. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 25 (4d8 + 7) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 25 (4d8 + 7) piercing damage plus 13 (3d8) acid damage.

Use Magic Item. He uses a magic item he has.