Ancient Mimic Dragon

Legendary Resistance (3/Day). If the mimic dragon fails a saving throw, it can choose to succeed instead.

Shapechanger. The mimic dragon can use its action to polymorph into an object or back into its true, draconic form. Its statistics are the same in each form. Any equipment it is wearing or carrying is transformed. While in its object form, the only attacks the mimic dragon can make are Bite and Acid Breath. It reverts to its true form if it dies.

Adhesive (Object Form Only). The mimic dragon adheres to anything that touches it. A Huge or smaller creature adhered to the mimic is also grappled by it (escape DC 22). Ability checks made to escape this grapple have disadvantage.

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

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

 Multiattack. The mimic dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 25 (2d10 + 14) piercing damage plus 14 (4d6) acid damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 21 (2d8 + 12) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 22 (4d6 + 8) bludgeoning damage.

Frightful Presence. Each creature of the mimic dragon's choice that is within 120 feet of the mimic dragon and aware of it must succeed on a DC 21 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 120-foot line that is 20 feet wide. Each creature in that line must make a DC 25 Dexterity saving throw, taking 90 (20d8) acid damage on a failed save, or half as much damage on a successful one.

The dragon 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 dragon regains spent legendary actions at the start of its turn.

Detect. The mimic dragon makes a Wisdom (Perception) check.

Tail Attack. The mimic dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The mimic dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.