Boneyard

Bone Subsumption. When the boneyard deals damage to a creature with bone inside of it, the target must succeed on a DC 16 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the creature finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. For each target subsumed, the boneyard's current and maximum hit points increase by 2, multiplied to the power of the target's number of size categories above Small, until it reaches its hit dice maximum of 306. If the boneyard's hit point maximum is at least 296 and it subsumes the bones of a creature that belongs to at least the Large size category and is at least CR 10, it becomes a dread boneyard, keeping its current hit point maximum.

Summon Minotaur Skeletons (1/Day). As a bonus action, three minotaur skeletons emerge from the body of the boneyard. A skeleton summoned in this way treats the boneyard as its master, and follows its orders to the best of its ability. The boneyard's hit point maximum is reduced by 4 for each skeleton summoned until they are reabsorbed. After 1 hour, the minotaur skeletons can spend an action to touch the boneyard and be reabsorbed into its body. The boneyard can be reanimated by reabsorbing any of these skeletons.

Multiattack. The boneyard makes three attacks: two with its bite and one with its tail.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one creature. Hit: 14 (2d8+5) piercing damage plus 7 (2d6) acid damage.

Tail. Melee Weapon Attack: +10 to hit, reach 15 ft., one creature. Hit: 12 (2d6+5) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the boneyard can't use its tail on another target.

Utter Subsumption. The boneyard makes one tail attack against a Large or smaller target it is grappling. If the attack hits, the target takes an additional 41 (8d8+5) acid damage. If this damage reduces the target to 0 hit points, the boneyard pulls the target's insides out, killing it instantly. The target's skeletal features (if any) are then absorbed into the body of the boneyard.

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

Move. The boneyard moves up to its speed.

Summon Skeletons (Costs 2 Actions). 7 (1d4+5) skeletons emerge from the body of the boneyard. These skeletons act on their own initiative count, and follow the boneyard's orders to the best of their ability. The boneyard's hit point maximum is reduced by 2 for each skeleton summoned until they are reabsorbed. After 1 hour, the skeletons can spend an action to touch the boneyard and be reabsorbed into its body. The boneyard can be reanimated by reabsorbing any of these skeletons.