|Series||The Grim Adventures of Billy & Mandy|
|Nano Item||Baseball cap|
|Voiced by||Richard Horvitz|
Billy comes from The Grim Adventures of Billy & Mandy. He is the dim-witted, big-nosed friend of Grim and Mandy, and the unwilling father of Jeff. His greatest fears are spiders, clowns, and the mailman.
During the war, Billy adopted a Fusion Spawn named Runty, which later turns out to be his imaginary friend. Most of Billy's missions are rather pointless, but sometimes lead to more important tasks: Once Billy had the player retrieve Irwin's stuff, so that he might "watch it." Other times he had the player collect food and cage lining for Runty, in doing so revealing Fusion Mandy's lair in the Sand Castle.
In his own interest, Billy sent the player out to remove the Re:Fuse posters found in Habitat Homes after being paid 20 bucks to do so by the leader of the Beautification Organization, Fusion Father. Little did he know that in doing so, he caused the local Fusion monsters to return to their normal destructive selves. Due to his fear of clowns and nightmares he'd been having, Billy has the hero go south to City Point, in order to defeat the Destroyusalls. He then has you collect their noses, but Billy thinks the noses are scary, so the hero gives the noses to Bloo.
Billy also tricked the player and stole his power of destiny, which allowed him to activate totems, just because he thought it was cool. Soon following Billy's attempt was Hex, who was unaware that Billy already had stolen the player's power. However, Mandy gives the player the Pillow of Common Sense, a strange pillow that actually took back the player's ability from Billy when the hero smacked him with it, and Mandy returns the player's powers to him (saying that she COULD have kept the powers herself, but decided she already had common sense).
In the last attack on a Fusion Control Center, Demongo planned to have Eduardo join the hero to provide an assault of Imaginary Energy. Billy showed up instead, thinking that the Control Center was the site of a party. He later showed up in Fusion Kevin's base under the same delusion. This time however, he was able to make himself useful by overloading a force field made from imaginary energy stolen from Foster's Home, allowing the player to defeat Fusion Kevin.