5x1 - The Grim Adventures of Billy and Mandy

When it's scurvy-prevention day at school, Mindy parades in her float in anticipation for the Little Miss Scurvy beauty pageant, and she insults Mandy, telling her she is ugly. To prove her otherwise, and with Principal Goodvibes' encouragement, Mandy considers entering the pageant. Naturally, Billy and Grim cannot believe Mandy when she tells them about the idea, but finally they decide to help her. Grim calls for Crabina, the Underworld's greatest makeup artist, to give Mandy a complete makeover. Crabina is shocked by Mandy's sour attitude, so she sets up principally to make her smile. At the pageant, Mandy has a real chance at winning the contest, but she still refuses to smile during her heart-warming musical number. Ultimately she smiles, but this event is so powerful that it alters the laws of the universe, and The Grim Adventures universe transforms into the The Powerpuff Girls universe, with Billy, Mandy and Grim turning into the Powerpuff Girls, Irwin turning into Mojo Jojo, and Professor Utonium guest starring as himself in a brief speaking cameo.