Ancient Mimic

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.

Amorphous Fate. Once defeated, an Ancient Mimic returns to its gelatinous state and the lair effects dissolve over a period of 1d4+2 weeks. However, if no effort is made to destroy the remaining gelatinous material using fire, the Ancient Mimic will regenerate in 1d6+1 days, and then either re-establish itself or move on to another suitable spot to create a lair.

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.

Reabsorb. As an action the Ancient Mimic may reabsorb any Lesser Mimic it can reach, living or dead, to regain Hit Points 14 (4d6+2). It may do this as a reaction if a Lesser Mimic is killed while inside it. It can not use Parthenogenesis for 1 turn after healing in this way.

Restraining Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d8) acid damage. Anyone attempting to leave the Elder Mimic's combat range or it's interior may be subject to this reaction. If hit, the target must make a Strength saving throw at DC 13 or be grappled.

Reabsorb. The Ancient Mimic may reabsorb any Lesser Mimic to regain Hit Points 14 (4d6+2) as a reaction. It may do this as a reaction only if a Lesser Mimic is killed while inside it. It can not use Parthenogenesis for 1 turn after healing in this way.

The Ancient Mimic can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The mimic regains spent legendary actions at the start of its turn.

Mutable Adhesion. The mimic changes the surface textures inside its lair, causing them all to become adhesive. The mimic adheres to anything that touches it, including creatures moving on its surfaces. 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. On a success, treat surfaces as difficult terrain. If you roll a 1 again at initiative 20, the mimic stops using it’s adhesive trait and surfaces revert to normal. You may spend 1 lair action to trigger this regardless of the dice roll.

Convulsion. The mimic convulses, forcing all non-mimics inside the room to make a Dexterity saving throw and succeed against a DC 14 or fall prone. You may spend 2 lair actions to take this action regardless of the dice roll.

Drag. The Ancient Mimic makes a Pseudopod attack against the target nearest the fireplace. On a successful hit, the target must make its DC 13 saving throw against Adhesive or be grappled. If the creature is already grappled, the creature is dragged 10 feet toward the fireplace. Once it reaches the fireplace the AncientMimic automatically makes a Bite attack. You may spend 3 lair actions to take this action.

Parthenogenesis (Recharge 5-6). The Ancient Mimic creates one new Lesser Mimic by separating one of the “objects” in the lair from itself, creating a new Lesser Mimic with Hit Points 18 (3d6 + 9) and AC 10. It enters the initiative tracker on the next turn and otherwise has the same stats as a Mimic found in the Monster Manual. No more than three Lesser Mimics can be active at any time.