3x18 - The Grim Adventures of Billy and Mandy

After watching a TV show, starring Captain Heifer and his Heifer Farms Brand Yogurt, Billy asks Grim to turn him into a superhero with the power of squeaking and throwing yogurt from his armpits. With his wish granted, Billy goes to outer space to fight the Evil Empire, but the planet he visits is mostly inhabited. Despite being free of Billy, Grim still has to deal with Billy's equally dumb father, Harold. After Billy fills the alien planet with yogurt, he returns home to be "normal".