Jabembuu, is Janemba and Super Buu fused. This happened while Janemba was wondering around hell and learned to go back in time. He wanted to find the strongest in the universe so he could be unstoppable. After he found Super Buu all alone they did the fusion technique that Janemba learned after seeing Goku and Vegeta performing it. The first thing that he did was to kill all of Hell's guards. He went back to his time and was able to pillage hell and escape with everyone looking for Goku who has already reached Super Saiyan 5.