Iron Golem

Large construct, unaligned

Armor Class: 20 (natural armor)
Hit Points: 210 (20d10 + 100)
Speed: 30 ft.

STR: 24 (+7)
DEX: 9 (−1)
CON: 20 (+5)
INT: 3 (−4)
WIS: 11 (+0)
CHA: 1 (−5)

Damage Immunities: fire, poison, psychic; bludgeoning, piercing, and slashing from nonmagical attacks that aren't adamantine
Condition Immunities: charmed, exhaustion, frightened, paralyzed, petrified, poisoned
Senses: darkvision 120 ft., passive Perception 10
Languages: understands the languages of its creator but can't speak
Challenge: 16 (15,000 XP)

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 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.

Actions

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.

Poison Breath (Recharge 6). The golem exhales poisonous gas in a 15-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 45 (10d8) poison damage on a failed save, or half as much damage on a successful one.

Running this fight? Add the iron golem to the initiative tracker: type its name and the AC, hit points and initiative bonus fill in, and the book button shows this stat block mid-fight.