Bone Golem

Immutable Form. The golem is Immunitie to any spell or effect that would alter its form.

Limited Magic Immunity. The Bone Golem can't be affected or detected by spells of 6th level or lower unless it wishes to be. It has advantage on saving throws against all other spells and magical effects

Magic Weapons. The golem's weapon attacks are magical.

Multiattack. The golem makes two  attacks.

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

Bone Prison- Bone golem can throw some of its bones at a creature within 30 feet—it must make a ranged attack to hit. These bones magically duplicate and form a cage surrounding struck creatures. Each round, the creature in the  cage makes a Dex saveing throw or take (2d10+5)   bludgeoning Damage. If the check fails, the target is still trapped but takes no damage. The target can escape the grapple normally, or can break out of the bones by dealing 15 points of damage to the prison, which has the same AC, and saves as the bone golem itself. Damage to the prison has no effect on the golem. The golem can only have one bone prison active at a time. If it wishes to create a second one, it (or some other creature) must first destroy the existing one.