Majin Buu was battling with Dabura, this battle ended by turning Dabura into a cookie biscuit. This resulta not just enemy defeating the enemy but Piccolo and Krillin transformed from statue to being back to normal. Majin Buu destroyed the earth by first, turning human citizens into candy and chocolate. Goku was terrified when he heard this.
In this fusion, Vegeta is the dominant influence. He is second only to Broly in power. Vegeto is able to hold off Evil Buu with ease, as a normal Saiyan (as apposed to a Super Saiyan), until Evil Buu transforms into Super Buu.
Due to Vegeta's influence on the character, Vegeto is often pertrayed as cocky, making the same mistake as Gohan in the Cell Games. This cockiness leads to Super Buu almost tearing apart the fabric of time and space.
The fusion earrings used to form Vegeto is the "proper" way to do fusion. So, the resulting fusion is of higher quality than the common Fusion Dance, meaning the end result has a much higher power level.
After Majin Buu was destroying cities every hour. Later in the saga, Majin Buu ate Piccolo, Android 18, Krillin, Commy, and everyone on the observatory?
Porunga's wish revived everyone including Krillin and Piccolo on the tower that were aten by chocolate.
Kid Buu is the final form of Majin Buu. He cannot be negotiated with. He has no remorse. He has no mercy. His sole reason for existence is to kill and to destory. And he enjoys it. This version resembles nothing less than a small Evil Buu. But he is far more powerful. Supreme Kai reveals that this is the original state of Majin Buu. Thousands of years ago Buu was confronted by the Five Kais. North Kai and West Kai were both killed by Buu whereas South Kai and Dakaiyo were absorbed. It was the absorption of Dakaiyo that turned Buu into the childish Fat Buu we initially see. South Kai and Dakaiyo however actually weakened Majin Buu because of their good influence. Now that they are gone and the original Buu is back he is a creature of pure Evil. His first target is the Earth which in a psychotic episode typical of him he blows up the minute his transformation is complete. Vegeta, Goku, Hercule, Dende and the puppy Bee are the only survivors. Kid Buu tracks them to the otherworld and engages in one last climactic battle with Goku and Vegeta. But Goku and Vegeta aren't strong enough. Hercule steps in and challenges Buu, but Buu finds himself unable to attack. Eventually he spits out something that turns into Good Buu. Hercule overcomes his cowardice to fight for his unconcious friend. When Good Buu wakes up he saves Hercule and then starts fighting Kid Buu. While this is going on Vegeta hits upon a plan. He has Dende, Supreme Kai and Elder Kai travel to New Namek where they summon Porunga, the Namekian dragon. Vegeta has them wish for the restoration of Earth and the resurrection of everyone killed since the morning of the World Martial Arts Tournament, except for the most evil. The Dragon complies. Goku is amused to find Vegeta is ressurected, pointing out this means his is no longer evil. Vegeta then explains his plan, a Spirit Bomb, made from the freely given energy of the people of Earth. He communicates to the entire planet via King Kai but only their friends and family believe him, the rest thinking it was all a dream. With the Good Buu now pounded into the dust Vegeta has to hold Kid Buu off so that the Spirit Bomb can be completed. Goku asks the people of Earth to help but only a few people Goku helped in the past give up their energy. As Hercule hears this he gets more and more angry until he starts shouting at the people of Earth who hear him. Hercule realises this and then proceeds to exhort them to give up their energy so that he can defeat Buu. He knows this is a lie and explains to Goku he doesn't believe they'd do it for anyone else. Thanks to Hercule the Spirit Bomb is finished but Kid Buu has defeated Vegeta who is now too weak to move. Kid Buu knows Goku wont fire the Spirit Bomb because it would destroy his friend and so he stands on top of him while he continues to blast Goku. Out of nowhere comes the Good Buu who uses the last of his strength to knock Kid Buu over and pin him. He tells Hercule to grab Vegeta. Kid Buu quickly recovers though and blasts the Good Buu but the way is now clear for Goku who fires the Spirit Bomb. But Goku is exhausted and Kid Buu is not only able to stop the Spirit Bomb, he is able to take control and fire it back at Goku. All seems lost until Vegeta asks Dende to make one last wish, to restore Goku's strength. With Goku renewed, he takes back control of the Spirit Bomb and directs it back at Buu. Buu tries to block it but it begins forcing him backward. For the first time his expression is one of fear, something he brought to so many.
Goku says 'It looks like this is the end of the road Buu. It's a darn shame. When I first met you, you were like a naughty little child who didn't know any better. But the battle between good and evil that was taking place inside you took place on the outside, and the darkness overpowered the light. From then on you changed. You were ruthless. You were a living nightmare and you enjoyed every minute of it.And that's why it has to be this way. You've got to learn what it feels like to have your life taken away against your will. It's wrong. Maybe you'll come back one day as a better person i hope. We'll have ourselves a little one on one. I'd like that.'
Goku then salutes his terrified adversary. 'Adios. See you on the flipside Majin Buu'
With that he triggers the Spirit Bomb. Majin Buu is engulfed. His expression is a mixture of overwhelming terror and agony. With one drawn out scream his body disintegrates and he is gone. This was the end of Majin Buu, the villain who caused more death and destruction than any other opponent the Z fighters faced. Goku later wishes on the Dragonballs for the people to forget about Majin Buu to allow the Good Buu to walk around without being feared. And ten years later at the World Martial Arts Tournament the Z fighters meet a boy called Uubu. This boy is the reincarnation of Majin Buu. Goku agrees to train him, and they fly away. This also marked the end of Dragon Ball Z