Majin Goku is a form Goku took after he was defeted by Vegeta. After this he goes on a rampage to kill everyone because of his loss. His power in this form is over SSJ3 meaning that he could beat Buu. Going for revenge,Majin Goku and Majin Vegeta fight. Under the influence of the Majin power,Majin Goku and Majin Vegeta can not control themselves and eventually end up destroying half of the north galaxy. He is one of the few Z fighters to turn Majin.