Shapechanger.  [Cursed] The mimic can use its action to polymorph, on a roll of Nat20, 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. It does not need to roll to polymorph into any held backpack item.

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 13). Ability checks made to escape this grapple have disadvantage. The Mimic may choose if and what it grapples.

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.

Got your Back!. The mimic has advantage on perception rolls if it is being worn as a backpack.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d8) acid damage.

Reactive Bite. If the mimic is being worn as a backpack, it can attempt to make a strength saving throw to reduce incoming damage by 1d8. Only if the enemy is attacking the target from behind. The mimic can only attempt to react if it can perceive the target.

Void Mouth. Whilst polymorphed as a backpack the mimic has the same properties as a Bag of Holding. If the mimic drops to 0 hit point, all its contents spillout before it makes any death saves.