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 13). 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.
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.
Corpse is an object.
So is a mannequin,
So if you find old enough mimic it could become NPC.
Edit: The older they are the more intelligent they become. All lore based.
I love these things for some reason!
good question
Not sure if you’ve already got a response to this; yes, but no. Mimics can only polymorph into medium or small objects. HOWEVER, Hoard Mimics can morph into huge objects. You would just have to give it a homebrew characteristic to let it morph into other things than treasure hoards.