Coal Golem

Blessing of the Forge. The golem has one of the following three traits, chosen by its creator:

Flame Body. Whenever a creature within 5 feet of the golem hits it with a melee attack, it takes 3 (1d6) fire damage and is burned as if it were hit by the Golem’s Fire Punch.

Flash Fire. When the golem would take fire damage, it can use its reaction to gain immunity to fire damage until the start of its next turn. While it is immune to fire in this way, the golem’s fire punch deals an additional 3 (1d6) fire damage on a hit.

Steam Engine. If the golem takes cold damage or has at least ten gallons of water splashed on it in one turn, it can use its reaction to increase its speed by 60 feet until the end of its next turn.

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 Fire Punch attacks and uses its Tar Shot if it can.

Fire Punch. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage plus 7 (2d6) fire damage and the target is burned. A target burned in this way deals only half damage with weapon attacks that use Strength.

At the start of each of its turns until the fire is put out, the burned target must make a DC 15 Constitution saving throw. On a failed save, it takes 3 (1d6) fire damage. On a successful save, the fire is put out. If the target or a creature within 5 feet of it uses an action to put out the flames, or if some other effect douses the flames (such as the target being submerged in water), the effect ends.

Rock Blast. The golem launches a blast of 1d4 + 1 rocks. Each rock flies in a straight line up to 90 feet in a direction the golem chooses before falling to the ground, stopping early if it impacts against a solid surface. If the rock would strike a creature, that creature must make a DC 15 Dexterity saving throw, unless that creature is prone in which case the rock passes over it. On a failed save, the rock strikes the target, knocks it prone, and stops moving. When the rock strikes something, the rock and what it strikes each take 3d8 bludgeoning damage.

Tar Shot (Recharge 5–6). The golem shoots a glob of sticky tar at a creature it can see within 30 feet of itself. The target must succeed on a DC 15 Dexterity saving throw or be covered in tar. While covered in tar, the creature’s speed is halved and it is vulnerable to fire damage. If the target or a creature within 5 feet of it uses an action to put scrape off the tar, or if some other effect washes it off (such as the target being submerged in water), this effect ends.

Earthquake (1/day). The golem casts earthquake (spell save DC 15).