Slag Slime

A burning amalgamation of living metal, the aptly named slag slime oozes across the landscape, reducing everything in its path ash. Appearing as a blisteringly hot pile of forge slag, these creatures are relentlessly destructive in pursuit of metal to feed upon. The heat that radiates from their bodies is so intense as to melt stone, flesh, and metal indiscriminately, making them rightly feared by all but the most fire-resistant creatures. Hungry for metal of all types, a slag slime melts down what it can find, adding the material to its own mass. Wherever these creatures are found, destruction follows, making them reviled and worshiped as a destructive aspect of nature.


Huge ooze, unaligned

Armor Class 21 (natural armor)
Hit Points 262 (21d12 + 126)
Speed 40 ft., burrow 40 ft., climb 40 ft.

27 (+7) 21 (+5) 22 (+6) 1 (-5) 14 (+2) 1 (-5)

Saving Throws Dex +11, Con +12, Wis +8
Skills Perception +14
Damage Resistances bludgeoning, piercing, and slashing from metal weapons
Damage Immunities cold, fire, poison, psychic
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, prone
Senses thermalsense (see traits) 120 ft., blind beyond that radius, passive Perception 24
Challenge 18 (20,000 XP)


Amorphous. Other creatures can enter the slime’s space, but a creature that does so is subjected to the slime’s Molten Slag feature immediately, and again at the end of each of its turns for as long as it remains within the slime’s space.

Legendary Resistance (3/day). When the slime fails a saving throw, it can choose to succeed instead.

Melt Magic. The slime is so hot that it melts magic itself. The duration of spells and magical effects with a duration greater than instantaneous affecting only the slime have their durations reduced to 1 round.

Molten Slag. At the start of each of the slime’s turns, everything within 15 ft. of it takes 14 (4d6) fire damage, standing water evaporates, and flammable objects in the area that aren’t being worn or carried ignite. A creature that touches the slime or hits it with a melee attack while within 15 ft. of it takes 14 (4d6) fire damage.

Additionally, if the slime reduces an object or structure made of metal or stone to zero hit points, it completely melts it, leaving a pool of molten slag in its space. This slag is considered difficult terrain and deals 14 (4d6) fire damage to anything that enters the area for the first time on its turn or starts its turn there. After 1 hour, slag produced by this feature cools becoming harmless but remaining difficult terrain.

Thermalsense. The slime can detect creatures within 120 ft. of it that are colder than the slime. Such creatures cannot be hidden from the slime.

Volcanic Tunneler. The slime can move through solid objects as though they were difficult terrain using its burrow speed.


Multiattack. The slime makes two attacks and takes one other action.

Harden (1/short or long rest). The slime rapidly cools its body, transforming its body into solid metal. While in this state, the slime is incapacitated, has resistance to all damage, its Molten Slag feature is suppressed, it cannot be critically hit, and regains 30 hit points at the start of each of its turns. The slime can choose to end this effect at the end of each of its turns, or until 24 hours as passed. Once the slime has used this feature, it cannot use it again until it finishes a short or long rest.

Creatures engulfed by the slime when it uses this action may attempt a DC 21 Strength saving throw. On a success, the creature escapes from the ooze and enters a space of its choice within 5 feet of the ooze. On a failure, the creature is incapacitated in addition to the other effects of being engulfed.

Envelop. The slime attempts to engulf a single creature or object completely in its space, forcing the creature to succeed on a DC 21 Dexterity saving throw, or become engulfed. On a successful saving throw, the creature can choose to be pushed 5 feet back or to the side of the ooze. A creature that chooses not to be pushed is engulfed. On a failed saving throw, the creature is engulfed.

While engulfed, the creature is restrained, cannot breathe, and has total cover against creatures other than the slime. If the slime moves, an engulfed target moves with the slime.

A creature enveloped by the slime can try to escape by taking an action to attempt a DC 21 Strength (Athletics) check. On a success, the creature escapes and enters a space of its choice within 5 feet of the ooze.

Expansion (3/short or long rest). Until the slime finishes a short or long rest, it increases its dimensions by 5 ft. in every direction.

Hurl Slag. Ranged Weapon Attack: +13 to hit, range 60 ft., one target. Hit: 14 (1d12 + 7) piercing and 10 (3d6) fire.

Pseudopod. Melee Weapon Attack: +13 to hit, reach 20 ft., one target. Hit: 18 (2d10 + 7) bludgeoning damage and 10 (3d6) fire damage. If the target is a creature, the slime may grapple it (Escape DC 21).


The slime can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The slime regains spent legendary actions at the start of its turn.

Expansion (Costs 2 Actions). The slime takes its Expansion action.

Squelch. The slime moves up to half its speed.

Strike. The slime makes a single attack.

Ref: TPKB1 p181