The Grim Adventures of Billy & Mandy is a fighting game based on the television series of the same name. It was developed by High Voltage Software and published by Midway. The PlayStation 2 version's DVD compatibility feature came with behind the scenes footage and the season one episode "Little Rock of Horror". The game was released on many Nintendo consoles in the United States, but only on the Wii in the United Kingdom.
When Grim's Mojo Balls get unleashed into Endsville, causing normal people to senselessly beat the tar out of each other (according to Grim, anyone touched by a Mojo Ball will be infected by supernatural rage), it's up to Billy, Mandy, Grim, Irwin and all of Endsville to save the world. They trek through places from their episodes such as the underworld, the pumpkin patch, even Billy's backyard. In the end, it turns out that Billy is to blame for the release of the Mojo Balls (he wanted to free Moe and Joe) and is severely punished by Mandy in the end credits (she mentioned that she hoped if the game had a mode which she and the others could just beat on Billy). During the credits you get to play as Mandy and beat Billy senseless with a flamethrower, melee attacks, and thor's hammer. (This is the only point in the game where Billy does nothing to cause damage to the player in return).
The gameplay heavily mirrors that of the Power Stone series. In the game, you can execute light and heavy style attacks. Gameplay includes 2-4 player Multiplayer, solo, and co-op Story Mode and Mission Mode. The environment is very interactive, with the ability to manipulate many objects. There are different weapons scattered through all the levels, such as a halberd or a club. Treasure chests contain a variety of items including weapons, cupcakes, hamhocks (which restore health), and Mojo Balls that fill up your Mojo Meter. When the Mojo Meter fills once, a Mojo Smackdown can be performed, where the character attacks the opponent with a barrage of punches, kicks, and slaps, finally destroying the opponent with a piledriver. When the Mojo Meter fills twice, a Mojo Meltdown can be performed, instantly knocking out all opponents. Each round of fighting begins with banter from each character on the playing field. An opponent isn't fully defeated until their lives are depleted AND the player or another opponent attacks them, triggering a 'finishing blow' sequence, in which whoever hits them has to do 4 finishing blows, knocking that opponent of the arena and the game. In Story Mode, the game culminates with a battle against the brain-eating meteor from Little Rock of Horror.
Source: Wikipedia, "The Grim Adventures of Billy & Mandy (video game)", available under the CC-BY-SA License.