He is all alone, so he tries to plot a fight with Vegeta. When he does Vegeta says why are you doing this? He said because it’s not right! Majin Goku goes Super Saiyan and punches Vegeta in the face. Then Vegeta turns Super Saiyan and does a Final Flash to Goku. Then when Majin Goku got hit, he did a 1,000,000,000X Kamehameha to Vegeta and Vegeta dies. And when he killed him he said what have I done? Then, he self-destructs to go to Other World to say sorry to Vegeta and explain to him why he was jealous, but Goku is not a Majin anymore but he still goes to Hell seeing as he once was possesed by evil.
1,000,000,000 X Kamehameha