The Lava Demon is a fusion of Fumos & Monica together
They only fuse if they're falling in the volcano (yes since Monica is lava poof), once they fuse. They climb outside the volcano & roar very loudly, telling them that The Legend of The Lava Demon is true (I'll post the legend later)
The Lava Demon is actually based on The Temple Gem Obsidian because the design & color. The Lava Demon has 7 eyes (3 on each side while the 7th eye is a third eye that rarely opens), They can also lava bend, summons volcanoes & etc.
It's all started when Fumos & Monica swimming inside the volcano, they accidentally fuse in the lava & form The Lava Demon (I wanted to rename it "Lava Giant" but Monica is 65% Demon)
Monica's gang went panic mode after seeing them as a fusion giant, they only talk in sign language. Both Nina & Wesley knows sign language because of their grandmothers
Nina & Wesley translate & said that their name is The Lava Demon, making Dly, Maxwell, Sam, Shadow, Joy, & Roy understand everything they sign
They're very tall for a lava demon, they're are 12'9 feet tall
Unlike Obsidian, they only have 2 arms and the hair is made of lava
DO NOT MESS. I repat, DO NOT MESS WITH THIS FUSION OF A FIRE ELEMENTAL & A DEMON