Ben 10: Ultimate Alien Episode 1.17 Nor Iron Bars A Cage

With Kevin having absorbed the Ultimatrix's aliens and gone back to his insane state, he returns back to the old Null Void prison. Ben and Gwen, searching for answers, realize they have to go to the prison in an attempt to stop Kevin from destroying the warden, Morgg. There are also flashbacks that Kevin has, how he left his first mutation and started to absorb solid matter both with the help of a fellow inmate named Kwarrel, and showed how he escaped from the prison, with Kwarrel sacrificing himself to Morgg in the process. Ben and Gwen soon realize that Morgg is forcing the prisoners to mine a blue substance which is sold as a hallucenagenic drug. Kevin manages to catch up with Morgg to exact his revenge, dropping him in an elevator and cutting the line. Gwen saves him and take him into custody, but by the time they hit surface, the prison is in ruins. Kevin has fled the prison, and Ben thinks that Kevin may have to be put down, much to Gwen's shock and horror.