Boneyard of Kyuss

Undead Nature. The Boneyard doesn’t require air, food, drink, or sleep.

Fast Healing. The Boneyard regains 10 hit points at the start of its turn if it has at least 1 hit point.

Bone Subsumption (Recharge 5–6). When the Boneyard hits a creature with its bite, the target must succeed on a DC 20 Constitution saving throw (undead make a Wisdom saving throw) or suffer 7 (2d4) damage to Strength, Dexterity, and Constitution scores. If any one of those scores is reduced to 0, the creature dies and cannot be resurrected except by wish or true resurrection. This effect only applies to creatures with a skeletal structure.

Utter Subsumption. If the Boneyard starts its turn grappling and restraining a creature with bones, it may attempt to finish the subsumption. The target must succeed on a DC 20 Constitution saving throw or have every bone in its body violently torn out and absorbed, instantly killing it. On a successful save, the target remains grappled and restrained. This is a magical effect. Creatures without bones are immune.

Inescapable Craving. If the Boneyard goes 24 hours without consuming bones, it must succeed on a DC 18 Wisdom saving throw or take 1d6 psychic damage and suffer disadvantage on Wisdom (Perception) checks for the next 24 hours. This effect stacks until it feeds.

Summon Skeletons (1/Day). The Boneyard summons undead servants. It can choose to summon 1d4+2 Troll Skeletons or 1d3+1 Young Red Dragon Skeletons. They appear in 1d10 rounds and remain for 1 hour or until destroyed.

Multiattack. The Boneyard makes two attacks: one with its Bite and one with Slam.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 28 (3d10 + 9) piercing damage. If the target has bones, it must make a DC 20 Constitution saving throw or be subject to Bone Subsumption if the ability is available.

Slam. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 25 (3d8 + 9) bludgeoning damage.

Grasping Clutches. If the Boneyard hits a creature with its Slam attack, it may attempt to grapple the target (escape DC 20). While grappled in this way, the target is also restrained.

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

Detect (1 Action). The Boneyard makes a Wisdom (Perception) check.

Slam (1 Action). The Boneyard makes one Slam attack.

Lurching Sweep (2 Actions). The Boneyard swings its massive body in a wide arc. Each creature of the Boneyard’s choice within 15 feet must succeed on a DC 18 Strength saving throw or take 11 (2d10) bludgeoning damage and be knocked prone.