Super 17

Super 17 is the powerful fusion of Android 17 and Hell fighter 17.

Early conception
After the evil Baby is killed by Goku, peace is thought to have been finally restored. However, in the depths of Hell, two master-minds worked on a horrific plot. Dr. Gero, the evil brilliant scientist who was responsible for all of the androids, and Dr. Myuu, who was responsible for the completion of Baby, teamed up to create the ultimate being. They decided that by merging the normal Android 17, with a machine mutant that they created in Hell, they could create the ultimate android killing machine. Super 17 attacks Vegeta. Myuu and Gero then used the machine mutant clone to brainwash 17 into joining them, first using both 17s to sync their energies together to open the gates of Hell, allowing themselves and mostly all other previously destroyed villains to escape. The real 17 then asked his twin sister Android 18 to join, but would wind up killing Krillin when he tried to contradict the mutant clone's voice in 17's head, then fending off 18's attack with relative ease. A short time later, 17 reaches his Hell Fighter counterpart, interrupting the latter's fight with Vegeta, at the same time as the Z Fighters.