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.

Deceiver (Humanoid Form Only). The mimic possess minimal psionic powers. When looking at it glancing directly into its eyes caused a creature with a least 8 INT to be stunned needing a WIS DC 13 to escape.

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

Consumer. The mimic has advantage on reaction attack rolls against any creature small or smaller, it possess the ability to unhinge its jaw and can devour creatures who are small and smaller.

Flailing Limbs. 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.

Acid Spit. Ranged Weapon Attack: +5 to hit, range 5/35 ft., area of effect of 15 ft., creatures in the area of effect must make a DEX save DC 16, on success that creature must move at least 5 ft. in escaping the AOE.  On failure, a creature suffer 1d10+2 acid damage.

Improved False Appearance (Object Form Only). As a bonus action an Apex Mimic can take the form of any object it can see however it can only hold this form to the start of its next turn.  If an attempted attack is made on the object that the mimic has duplicated the attacker has a 50% chance of guessing wrong, on a wrong guess the Apex Mimic can take a reaction attack.

Head Bash. Unarmed Melee Attack: +3 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d4) acid damage.