“Billy and Mandy vs. the Martians” When Billy destroys Grim’s favorite childhood toy, Fancy Jake, Grim feels devastated and wishes he had never lost the limbo game that made him become Billy and Mandy’s best friend forever and ever. A lawyer appears saying that although the game is legally binding while all parties remain on Earth, it is not if Grim leaves Earth. In consequence, Grim follows the lawyer’s advice, opens a mystical portal, and leaves. With Grim traveling aboard his spaceship, the lawyer takes off his disguise and introduces himself as Morg, the Martian Grim Reaper, who is also Emperor of Mars and commands an army of martian, brain-eating zombies. So Grim can get the respect he deserves, Morg convinces Grim to conquer Earth, which they do easily while enslaving and turning all of the people into zombies. Next for the reapers is to use the ultimate weapon in mind control, the Braincaster, which, if powered by a dumb and stupid mind, will allow them to control all of the zombies forever. Meanwhile, Billy, Mandy and Irwin, who followed Grim to Mars hidden in his bottomless trunk, look for a way to save Earth. When the kids are captured, and Billy is strapped to the Braincaster, all hope seems lost. Billy talks to Grim about friendship, and Grim has a change of heart and decides to help Mandy. Billy’s stupid, idiotic brain overpowers the Braincaster, returning all of the people to normal and foiling Morg’s plan, who disappears into outer space.