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.
Other mistake: Throughout the whole show there are several shots of submarines, aircraft carrier landings, chopper flights that are exactly the same in different episodes.
Other mistake: When Tom is sitting in the chair reading Ellen Combs' medical/surveillance file, the page he is reading just contains the lyrics from the Ella Fitzgerald song "Someone to Watch Over Me".