Adamantine Golem

Fire Absorption. Whenever the golem would take fire damage, it takes 0 damage and regains an equal number of hit points.

Unchanging Form. Spells or effects that would attempt to magically transform the golem or alter its shape fail immediately.

Magical Resilience. The golem has advantage on all saving throws made against spells and other magical effects.

Adamantine Plating. Its armor is so tough that any critical hit against the golem is treated as a normal hit.

Magical Attacks. The golem's attacks are considered magical for the purpose of overcoming resistances and immunities.

Multiattack. The golem makes $2$ attacks, which can be any mix of its Greatsword and Fiery Bolt attacks.

Greatsword (Melee). $+12$ to hit, reach $10$ ft., one target. Hit: 24 (3d10 + 8) slashing damage plus $10$ (3d6) fire damage.

Fiery Bolt (Ranged). $+12$ to hit, range $120$ ft., one target. Hit: $44\; (8d10)$ fire damage.

Poison Breath (Recharge 6). The golem releases a $60$-foot cone of noxious gas. Creatures within the cone must make a DC $18$ Constitution saving throw. On a failed save, a creature takes $55$ (10d10) poison damage, or half as much on a successful one.