Buu is a monster that has different forms and shapes. He is ressurected as Majin Buu. Majin Buu killed millions of Miis. Soon, Good Buu inside of Majin Buu expeled all the evil out of him. Good Buu and Evil Buu seperated, killing Majin Buu. Evil Buu fought Good Buu and eventually absorbed him, becoming Super Buu (When Good Buu absorbs Evil Buu, he becomes Majin Buu). A scrawny little Mii named Aurell returns from Heaven and a halo on his head, he reaches a new form, Ultimate Aurell. Aurell beats Super Buu with no problem. Buu absorbs Aurell while he is distracted, becoming Aura-Super Buu. Buu is then sliced in half by Mario Jr., letting out all the people he absorbed, and becomes Kid Buu (his original and most purest form). He promised he wouldn't hurt anyone ever again. He was wished to die and come back to Earth as a good human and noone would remember the events of Buu.
Majin Buu- Obtained when Good Buu absorbs Evil Buu.
Good Buu- All the good in Buu turned into a being of energy.
Evil Buu- All the evil in Buu turned into a being of energy.
Super Buu- Obtained when Evil Buu absorbs Good Buu.
Aura-Super Buu- Obtained Aurell is absorbed by Super Buu.
Kid Buu- Used when sliced in half and all the people he absorbed left out his body.