Shapechanger. The mimic can use its action to polymorph into a four, six, eight, ten, twelve, or twenty-sided die 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 Gargantuan or smaller creature adhered to the mimic is also grappled by it (escape DC 6). Ability checks made to escape this grapple have disadvantage.  The mimic can grapple only one creature at a time.

Damage Transfer. While attached to a creature, the mimic takes only half the damage dealt to it (rounded down), and that creature takes the other half.

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

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

Roll Control. When a creature grappled by the mimic rolls any number of dice for an ability check, attack roll, damage roll, or saving throw, the mimic can choose one of the die and cause the number the die rolls to be a 1.

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