The Grim Adventures of Billy and Mandy Video Game is the only
Billy and Mandy console game ever made. It was released for the PlayStation 2 and Nintendo GameCube on September 25, Game Boy Advance on October 16 and on Wii November 16, all in 2006. It was released for the Wii in Europe on March 16 and in Australia on March 15, both in 2007. It is a multiplayer platform fighting game with a story mode, VS mode, and side missions.
The home console versions are fighting games, with gameplay inspired by the Sega Dreamcast classic "Power Stone". On the game, characters can peform light and heavy attacks (with both ground and aerial variants of both), pick up and throw other players into danger zones, and use items, stage elements and weapons to turn the tide of the battle. The main power-up of the game are the Mojo Balls, which when collected 5 of them, allows the character to perform a Mojo Smackdown, in which they deal a massive flurry of attacks on a single opponents until all of their HP is drained. Once 10 Mojo Balls are collected, the character instead perfoms a Mojo Meltdown, which is a super devastading finishing move that takes a life from all of the opponents currently on the battlefield. Once an opponent runs out of lives and enters a dizzy state, the player must attack this opponent and peform a four-button quick-time event combo in order to eliminate them from battle.
The Game Boy Advance version, however, it's a beat-them-up platformer, in which only Billy, Mandy and Grim are playable, and must defeat enemies and clear missions in order to collect the Mojo Balls, which serves as both a power-up and the main collectible of this particular version.
You may start playing as Billy, Mandy, Grim, or Irwin, and start the game in Asgard. Someone released dangerous Mojo balls from Grims trunk, and they set off to find out who. They beat up Irwin in Asgard, but find only a chicken feather, leading Mandy to believe it to be Jack O' Lantern. They defeat him and for unknown reasons, head to the Underworld. They take down Nergal and Nergal Jr. and find more chicken feathers, taking them to the mutant chicken farm from a previous episode, Which Came First? Grim believes that they will find who did it at Billy's house, leading to a climactic battle with the Brain-Eating Meteor. Afterwards, it was Billy leading a trail of chicken feathers from a curse Grim put on his trunk giving Billy a chicken tail. He was digging in grim's trunk to free the mojo balls thinking there names were "Mo" and "Jo". It then goes to the credits where you can play as Mandy, beating up Billy. (HE IS SO STUPID!)
- Mogar (Harold): Finish story mode with any of the starters
- Eris: Finish story mode with any of the starters
- General Skarr: Complete mission 6, Tier 4
- Chicken: Complete story mode with all characters and play for 10 hours
- Nergaling: Complete story mode with all characters
- Viking: Complete story mode with all characters and destroy MOST letters in the credits
- Clown: Battle 100 times in VS Mode
- Pumpkin: Complete story mode with every character and get 100,000 damage points in VS mode
The game has 8 stages, with some that can be divided in 3 acts, totalizing 20 stages.
- The Afterlife (Fight For Your Afterlife): This stage starts out on an Egyptian tomb, where you can press buttons on the ground to actiavte traps that damages your opponents, such as spears sticking out of the ground, a cage and flamethrowers. Eventually, debris will fall down, "killing" all of the current players and transporing them to the Mead Hall in Asgard, where you can use a stuffed pig as a turret to shoot apples at your enemies. Finally it ends in the Battlefield, where a ballista can be mounted to shoot arrows, and rocks may fall down from the sky. This is Irwin's home stage.
- Pumpkin Pickle (Orange Terror): You start out on the Pumpkin Patch, where a lake with electrified eels, beehives filled with dynamite, graves and pumpkin demons await you. Once you escape, you now head to Downtown Endsville, where a giant pumpkin will slowly march through the city and smash everything on its path. Make sure to make good use of the chem-kill turret and radioactive waste cans. Eventually you will reach the Rooftops, where a high-voltage electrified sign, a wrecking ball, a plane containing a machine gun and the giant pumpkin will make your life a misery. This is Jack's home stage.
- The Underworld (Deep in Evil): Starting out on the entrance to Nergal's house, a pool of lava will make sure that you are burned to crisp. Eventually a giant snake will appear and break the barrier between the Underworld and the lava, and the whole place will start to flood. You must mount the giant snake's back in order to escape, but be careful with freeze ray shots coming out of nowhere. Once you land on a place full of castle debris, be wary of the mishcievous Nergalings that habit the place. This is Nergal and Nergal Jr.'s home stage.
- Clucking Doom: The level begins on the Mutant Chicken Laboratory, where you must avoid freee ray blasts, electrified floors and giant chickens coming out of the walls. You then make your way into the volcano's core, where a lava pit will cook you alive, and a mech will be sitting there awaitng someone to take posession of it. Once the place starts flodding, head to the elevator to be shot for the school bus, where a ernourmous chicken will be chasing it down the Highway, and multiple police cars, militairy tanks and trucks are trying to run away from the poulrty beast.
- Some of this game's defeat quotes and opening taunts are references to the show, except for characters that did not appear alongside each other (like, for instance, Nergal Jr. and Fred). For example, in the intro to Evil Con Carne, General Skarr's profile says that he enjoys kicking puppies as one of his hobbies, which he declares in the game as an opening taunt.
- Some quotes are references to other media, such as Mogar singing "Me, rock you like a hurricane!" (a reference to Scorpion's "Rock You Like a Hurricane") or Irwin crying "For the horde, yo!" (a reference to the MMORPG World of Warcraft).
- No character can go into Billy's Backyard outside of Story Mode.
- The song "Darkness" by SPF-1000 heard in Battle of the Bands is present in the credits.
- In an early version of the console release, Billy's Backyard (the final Story Mode Stage) had two players fighting. This could mean that the Story Mode could have had a co-op option, or that the stage could have been playable in VS Mode.
- Also, in several trailers and the demo shown if you leave the game remaining for a few minutes, the character icons are shown to be a bit bigger (and slightly different in some cases), and the wig in Grim's clown costume actually resembles what it looks like in the show. The reason for these changes is unknown, particularly the latter.
- While most costumes are based on events from the show, some costumes made their debut in the game (like Eris's goth outfit or Lord Pain's cowboy costume).
- There are two references to Conan the Barbarian's famous "what is the best in life" quote. One is Billy's victory quote against a viking, and the second is in Mandy's "likes" section on her bio.
- In the disc's internal files, it is revealed that the working title for the game is "Grim: Destroy Us All!"
- Mandy's model in the beta was different than in the final game. She has a smaller head, a bigger torso and her eyes were closer together.
- The song "The Rooftop" is written in the same tune as the Grim & Evil theme song.
- According to the game's files, Gladys, Sperg, Pud'n and Mindy were planned to be playable, but were scrapped. Mindy would end up being playable in Billy The Kid Fighting.
- The Xbox and Microsoft versions of this game was planned but it got cancelled for unknown reasons.
- In each stage, Pud'n can be found as an easter egg, generally on a very dangerous predictament.
- Jeff is the only member of Underfist that isn't playable, although he does make a cameo on concept art for said show. On his tumblr blog, Maxwell Atoms said that he was planned to be playable at some point, but was scrapped because he had a unique skeleton that would’ve required its own set of animations. Despite this, he's still credited as the voice actor for him in the game's IMBd page.
- Mandy's bio state that she could beat up a thousand monkeys with a thousand typewriters when given enough time, a reference to the Infinite Monkey Requiem.