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.
My Best Friend Is Invisible - S3-E2
Audio problem: When Brent is dribbling the basketball, it's very obvious that the sounds of it hitting the ground are not in synch at all with how Brent is bouncing it.
Audio problem: When Brian escapes his room and the headmaster with security is checking the rooms, if you look very carefully while the camera is going to Brian's room, you can see the headmaster hitting the door with his hand out, but the sound sounds like it would if he were hitting it with his fist.
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.