Trevor the Gross is hired as a substitute for Gonzo the Great, when Gonzo plans to leave The Muppet Show in Episode 411 to become a movie star in Bombay. Trevor is suggested by Scooter, due to both his own oddness and the fact that he's the best friend of J.P. Grosse (a relationship perhaps hinged on their homophonic surnames).
Gonzo spies on Trevor as he flirts with Camilla the Chicken -- but it's the last straw when Trevor steals Gonzo's act, singing "Top Hat" as he tap dances in a vat of oatmeal. Gonzo rushes onto the stage, aghast that this interloper is attempting his artistic feats, and Trevor, under duress from an enraged flock of chickens, gives up the spot. However, he does join the other Muppets for a heartfelt performance of "United We Stand."