This page we've got a quick look at what Kill Boy can do. He can grow his arms out and cover them with horrible spikes and blades and whatnot. If he were to hit you, it would be like being hit by John "Bones" Jones if ole' Bones's long arms were covered in horrible spikes and blades and whatnot. His ability is similar to how Cactus Joe could turn one of his arms into a horrible, massive claw when he was angry. Whereas the Clown's ability was born from his Demonic Blood, Kill Boy has a natural mutation that occurs from being born a member of the Lost Tribe. Maybe I'll talk about that more some day. Maybe. The idea was also somewhat inspired by the character of "Captain" Eustace Kidd from Eichiro Oda's "One Piece". So there's that.
Of course, as proof of how horrible a writer I am, Kill Boy gets Stopped before he can even show off his newly revealed ability. Poor Kill Boy is starting to end up like that one guy in "Police Academy" who loved violence but always showed up too late for the action. What was that guy's name?