In "The Lonely Mutation of Baxter Stockman," Shredder became weary of Stockman's poor progress in making effective mutant warriors and activated the mutagen collar on him. As the result of a housefly landing on his nose before the collar exploded, Stockman mutated into a humanoid mutant housefly with a lobster-like black claw for a right hand, a vertical mouth releasing an acid that dissolves metal, heightened hearing and superhuman flight speed that dubbed himself Stockman-Fly. Though he was a far more competent threat in this mutated form, Stockman's attempt to secure retro-mutagen from the Turtles failed. Taken before the Shredder, he pledged complete loyalty to the Foot Clan, believing them to be his best chance at returning to his human form.