Ben 10 season 4 episode 8 :Ben 10 vs. the Negative 10 (Part 1)

The Tennysons pick up the grandson of another Plumber named Cooper, who is hitching a ride home with them. Meanwhile, a Plumber base at Fort Knox is robbed by the Circus Freaks and Sublimino. By the time the Tennysons find out, they are too late to help. They soon learn of a second robbery, this one run by Rojo (having gained a new cybernetic suit), Animo, Clancy (mutated into an insect), and Charmcaster. Max discovers that they are searching for the keys to the "Sub Energy", an extremely potent sub-atomic power source given to the Plumbers by an alien race. they lose the keys to the villains, and attempt to route them at the Mount Rushmore base, where the Sub Energy is stored. However, they find that the Forever King, joined by a subordinate and the villains that raided the earlier bases, has beaten them to it. He dubs his team the Negative 10 and sets them upon the Tennysons.