Joo-Joo hails from the distant Eastern Caverns, an isolated region completely unknown to the 99 caverns where Burpy resides. Like Burpy, Joo-Joo is a faithful companion and an ultimate fire-based weapon; extremely loyal to Junjie and his ancestors, being passed down from one protector to the next making him one of the most experienced slugs around. For centuries, he and Junjie's ancestors had used the ancient slugslinging art of Slug Fu to keep the Eastern Caverns safe. But one day, a threat came that even Slug Fu could not stop: an evil slug known as the Goon allied with the sinister Emperor. Junjie's battle with these evil forces led them to the 99 caverns, where they joined the Shane Gang until they could return home to the Eastern Caverns and end the dark reign of the Emperor!
Joo-Joo debuts in "Ghoul from Beyond", Joo-Joo was the Darkfurnus in the possessed Junjie's hand when he was shown to Eli and Burpy. He was later fired against Burpy and created a huge explosion caused by him and Burpy. This led to a large dust cloud forming. He was later cured along with his owner when The Goon possessed Eli.
In "Return of the Elementals", Joo-Joo aids his slinger with helping the Shane Gang gather the Elemental Slugs before Dr. Blakk and Goon (now possessing Will Shane) do. At the beginning, he is seen practicing Slug Fu with Junjie. Later, he is used to with Burpy to hit the Goon but defeated by The Goon's Tempesto. He is later turned into a ghoul slug along with Burpy and along with the other fire slugs as the Fire Elemental slug was ghouled by the Goon but return to normal after Doc cured the Fire Elemental slug.
- Protoform Abilities - Small flame, good for light in dark spots, signal flares, lighting a camp fire.
- Flashfire - Shoots a small to medium fireball.
- Beatwave - Hits the ground surrounded by a giant fireball, knocking opponents back.
- Heatshield - Stops in mid-air, flame wings spread out and projects a protective wall of fire.
- Spikescorch - Extremely hot micro-comet projectile, good for piercing stone or steel.
- Flamespire - Spiral rings of fire surround an opponent.
- Novaclaw - Creates an exploding, fiery path.
- Wingburst - Stops in air with wings wide open and showers foe with fiery strafing.
- UpDraft - When exposed to the Slug Energy, turns blue and fire becomes blue fire (very hot perhaps) is still possible to mount it
- Like Burpy, Joo-Joo is a lone Infurnus wielded by a realm's protector.
- He seems to have a similar personality to Burpy, being the "leader" of his slinger's team of slugs.
- He and the rest of Junjie's slugs seem to know Slug Fu.
- Joo-Joo is the Infurnus of the Eastern Realms.
- Joo-Joo seems to be brighter coloured than Burpy, probably for viewers to identify which one is Burpy and which one is Joo-Joo.
- Joo-Joo has a little flame shaped mark on top of his head, instead of the lightning bolt mark on Burpy's head. This is likely for viewers to identify which one is Burpy and which one is Joo-Joo.
- In Ghoul from Beyond, Joo-Joo's Darkfurnus appearances looks the same as Burpy's; whether than having a "fireworks" kind of flame on his belly just like his normal mega morph protoform, he has the same flame as Burpy.
- Joo-Joo was the first one to actually megamorph over 2000 years ago, not Burpy.
- Joo-Joo is a boy but he can sometimes be mistaken for a girl.