William Pumpy is a main character in Stale Pancakes - 6th Grade.
First appearance was Halloween Speshul. Since then, he appears with Team Russia, teh main guys, with Roscoe, and with the team escaping the fading thing in End of the Earth. Since he was introduced so late in the series, he wasn't really that prevalent.
Bill has no known magical abilities - however, he does transform into his "ULTIMATE PUMPKIN MAN" form in Slime Invasion. Although, this was brought about by Nate's life-altering powers.
In said form, Bill's left hand becomes the head of a mace. His stem catches on fire, as do his eyes and feet. Then, he gains boots, which puts out the fire on his feet.
Bill is overly happy and fun-loving, and often pranks people (Halloween Speshul Pt. 1 and 2). He also, along with Roscoe, wants to get rich as fast as possible (Teh Diamond). However, these frivolous activities can get in the way of the law (all comics he's in).
Despite how careless these attributes make him, he loves Roscoe (no homo) very much (Slime Invasion).