Darkfurnus are the ghouled version of Infurnus slugs. One was first spotted in the Slugterra: Slug It Out! app during a cut scene right before you duel Locke and Lode in the 2nd chapter. But it officially makes its debut in the show in What Lies Beneath, where the Shane Gang must enter the Deep Caverns in order to stop the Darkbane, but they soon find out that their slugs won't work, so they have no choice but to ghoul them, and that would include Burpy. Then in "Slugterra: Ghoul from Beyond", Megamorphed Burpy would be turned into a megamorphed Darkfurnus by The Goon, and soon after Joo-Joo made make his debut (as a megamorphed Darkfurnus as well).
- Protoform Abilities - Small flame.
- Darkpyre - Dark fireball expands as it moves toward an opponent.
- Phallanx - Arrow shaped wall deflects or burns attackers.
- Blastfurnus - Shot into air, traps opponent in a domed birdcage of fire.
- Smashteroid - Mini-comet with trailing dark flame.
- Novacrow - Strafes an opponent with fire shot from slashing wings.
- Carrionbomber - Spirals above foe firing flaming ball blasts.
- What Lies Beneath (First appearance)
- Slugterra: Ghoul from Beyond (Megamorphed debuts)
- Slugterra: Return of the Elementals
- The Fall of the Eastern Champion
- Even though Burpy & Joo-Joo have different appearances, when they're turned in Darkfurnus(es), they're both megamorphed but they both look the same at velocity.
- Both their megamorphed Darkfurnus protoforms however are yet to be seen.