Grim Adventures of Billy & Mandy

The game's Story mode is a side-scrolling platformer/brawler where you control Billy, Mandy, or Grim as they try to stop the Mojo Balls from spreading. The gameplay alternates between small platforming sections and battles against enemies, which must be defeated before moving on to the next level. You can use kick, punch attacks, an air attack, and a special attack to defeat enemies, as well as a double jump and butt bounce action to navigate through the levels.

Defeating enemies fills your power bar, allowing you to unleash your special attack. The game also features boss battles at the end of each character's story, which must be completed to earn one Mojo Ball. There are three playable characters: Billy, Mandy, and Grim, with Billy initially available, followed by Mandy after completing his story and collecting a certain number of Mojo Balls.

Mission mode provides an alternative way to collect Mojo Balls, playing short levels with time limits that feel like mini-games. The game was released for the Game Boy Advance in 2006.