1) Gohan Buu is a good deal stronger than Janemba, because we see during the course of movie 12 that, while Janemba was stronger than him, Goku as a Super Saiya-jin 3 was at least able to deliver blows
First and foremost, I'd like to point out that the instance of Vegeta destroying the planet Arlia (actually everything involving Arlia) and the Ginyu Tokusentai appearing on North Kaiou's planet are scenes
1) The majority of that episode was what is known as filler, which in case you don't know is content in the anime that has no manga equivalent, and for the most part was not created by Akira Toriyama (but
1) This is one of the generally unexplained issues with the Cell Saga, since as you said, Cell points out that he's able to regenerate due to him having a nucleus in his head that allows and controls his
The Episode of Bardock is officially labeled as a spin-off, and is in no way canon to the main storyline of the Dragon Ball franchise. As you know, Bardock goes back in time, but exactly how he landed

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