Boney Stark

Multiattack. The bone lord makes two slam attacks.

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., One target. Hit: 15 (2d10 + 5) Bludgeoning damage. 

Powerful smash (Recharge 5-6). The bone lord makes a powerful sweeping attack with its massive arms. Each creature within 10 ft. of the bone lord must make a DC 16 dexterity saving throw or take 29 (4d12+5) bludgeoning damage and be knocked prone. On a successful save throw creature takes half damage and is not knocked prone.

Skeletal Assimilation. The bone lord is able to heal itself by reconnecting its lost pieces of bone. As a bonus action, the bone lord can slam a skeleton into its body, Regaining 15 hit points. The skeleton must have at least 1 hit point to regain hit points.

Berserk. If its creator falls unconcious or it drops below 20 hp, Boney will go berserk. In this state it has advantage on attacks, strength checks and ability checks and will attack the nearest thing to it, its creator must use an action to calm it DC15 Arcana Check.