Stench. Any creature that starts its turn within 5 ft. of the Mountain of Smiling Bodies must succeed on a DC 10 Constitution saving throw or be poisoned until the start of its next turn. On a successful saving throw, the creature is immune to the ghast's Stench for 24 hours.

Confusing Roar. The Mountain of Smiling Bodies may roar as an action when it can see any creature and isn't incapacitated. Each creature within 50 feet of the Mountain of Smiling Bodies and can hear the roar must succeed on a DC 16 Wisdom saving throw. On a failure, the creature can't take reactions until the start of its next turn and rolls a d8 to determine what it does during its turn. On a 1 to 4, the creature does nothing. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can't make such an attack.

Frightful Presence: Each creature of the Mountain of Smiling Bodies' choice that is within 30 feet of the dragon and aware of it must succeed on a DC 15 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 any Mountain of Smiling Bodies' Frightful Presence for the next 24 hours.

Consume. The Mountain of Smiling Bodies can create an additional limb from the bodies of small or larger creatures' corpses it consumes, granting it a slam attack (up to two) and healing 2d8 hitpoints. If The Mountain of Smiling Bodies consumes another creature while it has two extra limbs, one of its existing limbs will be replaced by the new one. The removed limb becomes a Gibbering Mouths (CR 2 Aberration)

Truesight. A creature with truesight can, out to a specific range, see in normal and magical darkness, see invisible creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceives the original form of a shapechanger or a creature that is transformed by magic. Furthermore, the creature can see into the Ethereal Plane.