Continuity mistake: The size and shape of the stain on Nicholas' shirt after he falls into the spillage, changes.
Audio problem: Towards the end of the episode just before Grace turns out the lights, Nicholas says "Ugh, now what?" but his lips are not moving at all, even with his head turned.
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.