Johnny Test (2005)

Season 6: Episode 14

Johnny is late to class again, and he gets a visit to the principal's office which unexpectedly leads into Johnny becoming the new hall monitor of the school, due to someone named the Speedster (who is literally a speedster) delaying kids from getting to their classes. Johnny interrogates the school bully Bumper, who reveals the Speedster to be Sissy Blakely, so he "borrows" Susan and Mary inventions to try to catch Sissy.