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

Immutable Form: The golem is immune to any effects that would alter its form

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

Magical Weapons: The golem weapon attacks are magical.

Multiattack: The golem makes two slam attacks.

Slam: Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d8 4) bludgeoning damage plus 7 (2d6) necrotic damage. 

Fire Shield (Recharge 6): The golem wreaths itself in flames for a minute, shedding bright light in a 10-foot radius and dim light for an additional 10 feet. The shield grants resistance to cold damage for the duration. In addition, whenever a creature within 5 ft. of the golem hits with a melee attack the shield erupts with flame. The attacker takes 9 (2d8) fire damage.