Shapechanger. The mimic can use its action to polymorph into a coin 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 any creature that it touches. A creature adhered to by the mimic is also grappled by it (escape DC 6); though if the creature is Small or larger, this grapple does not reduce its movement speed and when the creature moves, the mimic moves with it.  Ability checks made to escape this grapple have disadvantage.

Damage Transfer (Object Form Only). While it is grappling a creature, the mimic takes only half the damage dealt to it, and the creature grappled by the mimic takes the other half.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary coin.  A creature within 10 feet of it can discern its true nature with a successful DC 12 Intelligence (Investigation) check.

Flat Form (Object Form Only). Ranged attacks and opportunity attacks made against the mimic have disadvantage.

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

Pseudopod. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 1 bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

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

Coin Flip. The mimic flings itself up to 10 feet through the air towards a creature it can see.  That creature must make a DC 12 Dexterity saving throw.  On a failed save, the creature takes 1 bludgeoning damage.  If the mimic is in object form, the target is subjected to its Adhesive trait.  On a successful save, the mimic falls harmlessly to ground at the target's feet.