Attack Of The Mutant (1) - S2-E2
Other mistake: In part 2, it was revealed that Libby was really the Masked Mutant all along but, in one scene in this episode, Libby is sitting next to Skipper while the Masked Mutant is standing on top of the bus.
Revealing mistake: The eyes of the actor playing Gideon the robot can be seen through the eye slits of the robot mask in some shots.