At the end of the Dragon Ball Heroes anime episode 1, an evil saiyan with a straitjacket appears. Who is he and which dimension does he come from?
The evil Saiyan is Kanba and he only makes a short appearance in Episode 1 where Fu refers to him as the Evil Saiyan. In the games, Kanba is summoned with the help of the Dragon Balls which are used by Fu. They haven't revealed much such as where he exactly is from and the reason for obtaining that power.
The only information we have as of now is that he possesses an unbelievable strength even superior to SSJB Goku and SSJB Vegeta. The two of them had to Potara fuse and turn Vegito Blue to fight with him. In the games, Vegito blue had to stack Kaioken on top of his blue form to fight with Kanba.