Ass Pull: Jimmy's dad becoming a creature catcher after the episode "Ghost Bust a Move". We're expected to believe that an everyday man of average intelligence is able to invent fully working hi-tech gadgets used to capture not only solid creatures, but ghosts as well.
He doesn't make all those gadgets himself. At the end of the episode "Revenge of the Creature Catcher", after escaping from Scare School, Mr. Bradley calls a company named "Creature Catcher Supply" to order new gadgets for capturing all the students in scare school. Apparently, in the CSS-universe creature catcher is an official profession, and there are actually companies that produce the weapons and tools needed for this job.
Idiot Plot: The plot of "Vote for Casper" relies on Thatch and his friends tricking Casper and Mantha into believing they're each trying to sabotage the other's campaign.
Jerkass Woobie: Sure, Mosshead might be annoying and kind of an Ungrateful Bastard, but you can't help but feel bad for him when his family went to a condo development and wouldn't take him, leaving him homeless.
Ship Tease; The episode "The Day The Professor Croaked" teases both Nurse/Professor Burns and Kibosh/Hedy. When Kibosh accidentaly kisses Hedy's head/crystal ball neither of them, especially Kibosh, seemed bothered by it. He even passed Hedy for everything during the school's inspection just for her "perfect caligraphy" and seemed lovestruck until he left the classroom. The nurse also was more than happy to kiss Professor Burns to change him back to normal when everyone thought he had turned himself into a toad.
The Woobie: Wolfie, in some ways. He was a minor character in the second season, and now he is just a loner, and now isn't really a part of Casper's crew. In fact, he had a neutral relationship with them and becomes rather distant towards Casper and everyone else.