Ben 10 Omniverse: Season 5, Episode 3

5 - 3: Bengeance is Mine

Bill Gacks, an (actual) human plumber who resembles Vilgax (due to his beard), accidentally activates a weapon Vilgax set to attack Bellwood while fixing Pakmar's plumbing in Undertown. When Psyphon returns, he believes Bill is Vilgax, and, elated that his master has returned, pledges to help him in any way to destroy Bellwood. Meanwhile Ben and Rook try to stop Vilgax's squid monsters that the weapon accidentally released.