Punch. Creature hits opponent with fist.

Punch. Melee Weapon Attack: +5 to hit, reach 5ft., 1 target. Hit: 1 (1d4 + 4) [bludgeoning] damage. 

Grapple. Melee Attack: +5 to hit, range 5ft., 1 target. Hit: 1 (1d6 + 4) [bludgeoning] damage. Upon successful Grapple, if opponent cannot escape Grapple (DC 16 STR) on next turn Mimic can slam.

Slam. Melee Attack: +5 to hit, range 5 ft. 1 target. Hit 1 (1d8 + 4) [bludgeoning] damage. Opponent is prone. Upon failed Grapple escape, Mimic can Slam as an action

MImic. A mimic can assume the general shape of any object that fills roughly 150 cubic feet (5x5x6). Mimic will have a disguise check and player rolls a perception check to see mimic upon investigation. 

Flex. When a opponent glances heavily at the visible mimic when not engaged with another opponent, the Mimic will flex its muscles.

Attack of Opportunity

Spear. When Attack of Opportunity is presented, Mimic can launch itself towards opponent spearing them. DC 15 STR saving throw for opponent to prevent being knocked prone.

Kick. When Attack of Opportunitt is presented, Mimic can Kick opponent dealing (1d6) +5 to hit [bludgeoning] damage.