Chain Golem

Fire Absorption.  Whenever the golem is subjected to fire damage, it takes no damage and instead regains a number of hit equal to the fire damage dealt.

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

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

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

Fale Appearance. While the golem remains prone and motionless, it is indistingushable from a heap of chains.

Multiattack. The golem makes to Chain attacks. If both attacks hit a Medium or smaller target, the target is grappled(escape DC 18), and the golem uses its Engulf on it.

Chain. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 23 (3d10 + 7) slashing damage.

Engulf. The golem engulfs a Medium or smaller creature grappled by it. The engulfed target is blinded, restrained, and unable to breathe, and it must succeed on a DC 18 Constitution saving throw at the start of each of the golem's turns or take 23 (3d10 + 7) slashing damage. If the golem moves, the engulfed target moves with it. The golem can have only one creature engulfed at a time.

Whirling Chains (Recharge 6). The golem furoshisly spins four chains around it in a 15-foot circle around it. Each creature in that area must make a DC19 Dexterity saving throw, taking 45 (10d8) slashing damage on a failed save, or half as much damage on a successful one.