The Grim Adventures of Billy and Mandy
Season 4 Episode 19 - Runaway Pants
At school it is time for the "Presidents Fitness Test", but Billy is absolutely unfit for exercise. On the other hand, Nergal Junior uses his shape-shifting powers to become fit at will and excel in every test. Billy asks Junior to transform into a pair of pants that he can wear, so he can run fast and win the 50-meter race. Since Junior has never attempted to transform into inanimate objects he cannot stop running and cannot revert to his human form. Billy keeps running forever while he becomes a national sensation known as the "Fitness Lad". It is revealed that the story was just all a fabrication created by the narrator, who parodies The Twilight Zone.
Episodes in Season 4
The Secret Snake Club
He's Not Dead, He's My Mascot
Hog Wild
The Bad News Ghouls
The House of No Tomorrow
Happy Huggy Stuffy Bears
The Secret Decoder Ring
Wild Parts
The Problem with Billy
Wishbones
Dream Mutt
Scythe for Sale
Jeffy's Web
Irwin Gets a Clue
30 min