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.
Attack Of The Mutant (1) - S2-E2
Plot hole: Skipper spots the Masked Mutant's headquarters the first time he goes past. He then goes back the next day, and the headquarters have vanished. He then goes back a third time, and the headquarters aren't there yet again. However Skipper says "How can it be. It was right here yesterday," although it wasn't.
Attack Of The Mutant (1) - S2-E2
Continuity mistake: When Skipper and Libby are in the elevator, before it crashes to the floor, Libby backs up right against the wall. In the next shot as the elevator doors open, she is standing in the centre of the elevator.
Answer: Whoever created the Masked Mutant comics would still be around to create other comics even with the Masked Mutant dead and the Galloping Gazelle retiring, so Skipper could still receive different comics with all new characters. When Skipper goes into the Masked Mutant's lair, he is hit with a beam of light that turns him into a comic book character so after saying that he's the Colossal Elastic Boy, he turns into the hero at the end of the episode.