Ben 10: Ultimate Alien: Season 1, Episode 17 - ProjectFreeTV

1 - 17: Nor Iron Bars a Cage

With Kevin having absorbed Ben's aliens and become insane once again, Ben and Gwen have to go to the null void prison in an attempt to stop Kevin from destroying all the people there. We learn more about how Kevin got his material absorbing powers. In the end Ben thinks Kevin should be put down.