Revealing mistake: If you look closely, you can see human eyes inside of the mud monster's left eye. Pausing or slowing down is not required or necessary, but is easier to see if you do.
Night of the Living Dummy III (2) - S2-E25
Revealing mistake: When all the dummies are set up in Zane's room, you can see in many shots that what is meant to be Zane as a dummy is a complete human.
Revealing mistake: The rocks and tree trunks bend and give way under the weight of Cooper, after he and Fergie are pushed into the cave in the ground.
The Ghost Next Door (2) - S4-E4
Revealing mistake: In the montage of important scenes from part one at the start of the episode, when Danny Anderson falls into the bunch of garbage cans, the mask on the stuntman's face becomes undone and reveals him. (00:22:20)
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.