Bartman Begins is the second level in The Simpsons Game and the first level with the ability to play as a two player or switch characters (1P Only). In this level you play as Bart, and Homer in the Springfield Natural History Museum while trying to prevent Jimbo, Dolph, and Kearney from stealing the exhibits for Principal Skinner so that Springfield Elementary would have visual aides for their science classes. Now Bart, his Bartman powers, and Homer are ready to stop them.
This level also introduces Bart's Bartman power and (only in the PlayStation 3 and Xbox version) the ability to turn into "Robot Bart", his invincibility ability. Homer in this level cannot turn into the Homer Ball as he did for a brief time in the previous level and can only move around, activate switches, jump, and attack. This level also features Wiseguy and Sideshow Mel as security guards enemies and Jimbo, Dolph, and Kearney as mini-boss enemies.
Bart buys a copy of Grand Theft Scratchy: Blood Island but Marge comes and confiscates it from Bart and hides it in Homer's underwear drawer where she put his swimsuit magazines (possibly the Playdudes from "All's Fair in Oven War") and his BB gun. Bart then angrily walks into an alley when an instruction book to The Simpsons Game falls from the sky, which appears to be a lot bigger than the real one. Bart then discovers that his whole family are characters in the game and they all have powers. Bart reads his power is turning into Bartman.
Then Homer comes by with a swimsuit magazine and a BB gun that he found in his underwear drawer and then they decide to go in the sewer. Apparently the sewer leads up to the natural history museum. Bart and Homer then find out that Jimbo, Dolph, and Kearney are robbing the museum and decide to stop them. After Bart and Homer defeat some security guards on the way, Bart jumps to the top of a tree and uses his slingshot to drop dinosaur bones on Dolph. Then they get to a museum game in which Homer has to activate some targets in a window and Bart has to use his slingshot to throw rocks to them and scare Kearney, who is in the back of the window. After they knockout Kearney, they end up in the astronomy exhibit of the museum (from "'Scuse Me While I Miss the Sky").
Bart climbs a lot of platforms to get to a UFO at the top of a giant planet Earth representation where Jimbo is. Bart and Homer then knockout Jimbo. Principal Skinner then comes in and says he hired the bullies to steal the exhibits because they cannot get real science stuff for the school.
Soon Chief Wiggum arrests Skinner after arriving at the museum no thanks to incomprehensible directions from Mapquest.