Bone Sentry

Immutable Form. The Bone Sentry is immune to any spell or effect that would alter its form outside of its own will.

Magic Resistance. The Bone Sentry has advantage on saving throws against spells and other magical effects.

Magic Weapons. The Bone Sentry's weapon attacks are magical.

Multiattack. The Bone Sentry makes two slam attacks against a creature.

Slam. Melee Weapon Attack: +10 to hit, reach 10ft., one target. Hit: 23 (4d8 + 7) Slashing damage. 

Bone Coffin: 30ft. The Bone Sentry shoots a bony claw to grapple a targets of size large or smaller.The creature must make a DC 17 Dexterity saving throw. On a failed save, the target is pulled into the chest of the Bone Sentry and restrained. At the end of the creature's turn, it may attempt to break free from the Bone Coffin by succeeding a DC 20 Strength saving throw. The Bone Coffin can hold creatures as detailed below:

4 Tiny

3 Small

2 Medium

1 Large

Consume. The Bone Sentry may add any bones from surrounding corpses to itself within 10ft.

Extract. If a creature is restrained by the Bone Sentry's Bone Coffin, it may attempt to extract the bones from the trapped creature. The creature must make a DC 15 Constitution saving throw. On a failed save, the creature takes 6d6 slashing damage. On a successful save, the creature takes half. If this reduces the creature's hit points to zero, the creature dies and its bones are added to the Bone Sentry. This restores hit points as detailed below:
Tiny: Restores 5 Hit Points

Small: Restores 10 Hit Points

Medium: Restores 15 Hit Points

Large: Restores 20 Hit Points

Carpal Defense. If an attack hits the Bone Sentry or another creature within 10ft of it, it may shield the creature with its hands, increasing the Armor Class of the target by 4 until the end of the attacker's turn.