Cyborg Bart was what Bart became after harvesting robot parts to become a powerful cyborg.
Bart ends up in a coma after attempting to jump from the roof to the swimming pool at Spinster Arms Apartments. In an effort to cope with the loss of their boy, the family takes in a robotic boy, named David, who quickly proves to be a better son. Later, Bart is found to be alive, however the two boys soon try to compete for their families love. Marge grows concerned with the boys rivalry, Homer comforts her and says he'll fix it. Of course instead of getting rid of the better robot son Homer decides to dump Bart in the woods. Bart soon comes across a band of defunct robots, harvesting their parts while they are asleep. He returns home to seek his revenge on David, and in the end, he cuts both Homer and David in half. How exactly he replaced his real body with a robotic one is left unknown.