Bart vs. the Space Mutants is a 2D side-scrolling platformer.[1][2] In the single-player game, Bart Simpson is the only one who knows of the aliens' secret plan (his X-ray specs allow him to identify aliens in human form, based off of the sunglasses from the 1988 film They Live)[3] and he has to stop them from collecting the items they need to build their "ultimate weapon" to take over the world.[4] There are five levels,[1] in which Bart must collect or destroy a certain number of these items (purple objects in the first level, hats in the second, balloons in the third, exit signs in the fourth, and nuclear rods in the fifth).[4][5] If Bart loses a life he says "Eat my shorts!" Another objective of Bart vs. the Space Mutants is to help Bart convince the other members of the Simpson family about the aliens' existence so that they will help him during the levels.[6][7] This is achieved when Bart defeats a disguised space mutant, whereupon he collects a letter. Should he spell out the first name of a family member, said member will aid him in the boss battle. The five stages are the streets of Springfield, the Springfield Mall, Krustyland Amusement Park, a natural history museum, and the Springfield Nuclear Power Plant. If Bart exhausts all his lives, an end scene will be shown depending on what stage it took place, where the aliens gloat over their victory and/or mock Bart. If Bart completes the game, an end scene will be shown where the enraged aliens vow never to return to Earth, but try to accept defeat graciously and do something to pay their respects to the boy who thwarted them. Six months later, the Simpsons are vacationing in South Dakota when they notice a fifth face on Mount Rushmore that looks like Bart's.
In order to get to some of the items and progress through the game, Bart must use equipment such as rockets and cherry bombs, which are bought with coins that can be collected by getting rid of aliens.[5] Bart is controlled on foot and on a skateboard.[8] To get rid of aliens, which are disguised as real humans, he needs to jump on their heads, although some are just regular humans.[4] The game increases in difficulty with each level,[8] and Bart meets up with a boss at the end of the first four.[7] The levels use elements of The Simpsons and some of the television humor appears in the game: for example, in the first level Bart can make a prank call to the bartender Moe in order for him to run outside so that the player can spray paint his purple apron (an example of an item that the aliens need) into a red color that the aliens do not want.[9] The game includes some minigames.