Foomy arrived at the cabin via Kavonn's hat, and declared himself a "fire demon" when the confused warlock asked him what he was. As it turns out, Foomy had botched a suicide attempt after his best friend betrayed him and stole the girl he was in love with away. He threw himself into what was a fabled "Vortex of Death" (nobody returned from it, so it was assumed to kill anyone who got tossed in) and found out it was actually a wormhole, and the path took him to the portal connected to Kavonn's hat.
Menu took an immediate disliking to him when the sprite belched fire on him after helping himself to a bubbly Fiz soda. Foomy comes from a place where all its denizens are fire-proof, so setting the werewolf's hair on fire and having him scream and roll didn't register as "painful burning" and more like melodramatic theatrics.
Menu also doesn't like the fact that Foomy chooses not to wear clothing, being a furry animal creature that happens to be bipedal, Menu finds it somewhat indecent (never mind that he doesn't wear pants himself!) It was discovered that Foomy's explosive reactions to certain foods made pants-wearing a little bit of a fire hazard.
Foomy also gets away with his unwelcome stay by virtue of being "cute" to Claire, who would probably scold Menu for kicking the sprite into the street.
Foomy has formed a friendship with Kavonn's trio (Phineas, Crispo and Daray) and is loosely friends, but at the same time fearful/fascinated, with Mannick. It is also implied that he has a crush on the fairy Azelea .