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.

Headless.

The golem is blinded and deafened, giving it disadvantage on all its attack rolls, and it can't use its Poison Breath.

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.

Multiattack.

The golem makes two melee attacks.

Slam.

Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Sword.

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

Headless Iron Golem