The Simpsons have found all four keycards to open the door to the creator's mansion. After talking to their 8-bits counterparts (who ask them how many lives they needed to get here), they head in. The mansion is full of coins and Simpsons characters models. Homer and Bart decide to pee on his dollar sign-shaped trees before entering, but their creator, who turns out to be Matt Groening, watches them, so he sends his lawyers to attack Homer and Bart. They combat the lawyers using Homer's "Gummi-Homer" power and Bart's Bartman power. To their right there is a locked gate, which Bart opens by jumping and gliding on some posts with the lever. Beyond the door there is a large pool. Bart grapples to the other side and pulls a lever that electrifies the water, killing the sharks in the pool and allowing Homer to jump on them.
Homer, as Homer Ball, destroys a pole which they use to get to the other side of the pool. They reach the door to the house, but to open the door they have to solve a puzzle: stepping on a piano on the floor to make sound the Simpsons' theme, which opens the door. Once inside, they defeat more lawyers and go upstairs to a room with giant pencils in horizontal position in each side. They move and close the way and then open again, and is the moment for Homer and Bart to cross to the other side. Now they get to a large room, with big Simpsons statues on four pedestals and a big table on the center. They defeat more lawyers, and later step on a little button that turn on a light to a mirror. This mirror directs the light to another mirror on an upper floor. To reach it, they step on moving book shelves to the button next to that mirror. Now the light is directed to another one, and Homer jumps on moving platforms with big hammers to reach the other mirror. Now the other is on a high ledge.
They have to jump on the moving lights and float (Homer's "Heli-Homer" power) or glide (Bart's Bartman power). Once they reach the last mirror, a door on the last ledge opens, and leads them to Matt Groening's office. It is full of coin pills and Futurama (his other series) characters paintings. Matt is on his desk, on the highest ledge. He draws two Futurama characters, Bender and Zoidberg, who come to live and attack Homer and Bart. Once they defeat them all, Homer uses his Homer Ball power to boost on a coin pill and hit Matt Groening, who is on a balcony above. He lies on the floor, only to be kicked by Homer and Bart.
After Marge stops them, Lisa tells Matt how they dislike being video game characters. Matt seems to understand, but he doesn't care, since he presses the self-destruction button and goes away in his helicopter (after signing the window with his signature). All the game engine is collapsing and all the enemies and characters from the four worlds, and Mario from "Enter the Cheatrix", come out to escape. The only portal left is the one to Springfield so they all head in. A sign falls on Moe-orc (from "NeverQuest"), and although he resists the weight, the young Mr. Burns (from "Medal of Homer") tells him to wait to go for some paintings, so the sign splats Moe.
Back at the Simpsons house, the Simpsons and the characters see the aliens destroying the city, but Lisa has an idea about building a ladder to the Heaven using her Buddha's Hand powers to talk to God.
Five Characters in Search of an Author characters
Homer: Homer is one of the playable characters, he can jump, kick, burp, turn into Homer Ball, "Helium-Homer", "Gummi-Homer" and (only Xbox version) "Lava-Homer".
Bart: Bart is one of the playable characters, he can jump, kick, use his wrest rocket, open his cape to release bats and turn into Bartman to glade, climb walls and ziplines and grapple. He can also turn into "Robo-Bart" (only Xbox version).
Matt Groening: he is the main boss in the last part of the level. He changes positions and draws sketches of Bender and Zoidberg so they become real and attack Homer and Bart.
Blue-haired Lawyers: enemies throughout the level, except in the last part. They attack by launching papers through their bags and whacking with their suitcases.
Bender Bending Rodriguez: one of the main characters of Futurama. Multiple Benders are drawn by Matt Groening as enemies in the last part of the level to attack Homer and Bart by throwing beer bottles at them (only Xbox version) and wears a chef's toque (only PS2 and Wii versions)
Zoidberg: one of the main characters of Futurama. Multiple Zoidbergs are drawn by Matt Groening as enemies in the last part of the level to attack Homer and Bart by shooting ink balls to them. In the Xbox version these enemies do not have the ink shooting ability. Instead they attack Bart and Homer up close with their claws.