Based on how Kibosh used to be a friendly ghost with fleshie friends when he was Casper's age and Casper isn't afraid of him. Kibosh may have had a relationship with a woman who could become Casper's mother. The woman found out she was expecting Casper after breaking up with Kibosh due to him becoming unfriendly when he became the leader of the Underworld and since she didn't want her child to turn out like him she left him with her brothers, the Ghostly Trio to protect him.
Since they started out the same way Kibosh sees potential in him and being that Casper's the only ghost in the school, this seems to make him more intent on getting through to Casper.so he's going to keep trying to change him and make him the next ruler whether Casper wants to or not.
There are just too many contradictions between the two. In the movie, Harpy is seen in the Valley of the Shadows, but in the series she is a student at the school. The events from the movie are never mentioned in the series. And while the movie ends with the creatures and the inhabbitants of Deedstown setting aside their differences, they are all back to their old ways in the series.
And all episodes that came out afterwards are actually set before this 4-part special.
- Possibly, since one of the episodes has Jimmy's dad surprised to learn (again) his son is friends with monsters.
It may look like an Everytown, America, but there is no denying in that this particular town seems to have a very strong connection to the underworld. Every time the students of scare school go to the human world for a class trip or assignment, they always go to Deedstown and never decide to visit some other city for once. The manor of Casper's Uncles has a doorway that leads directly to Scare School. And even though monsters are frequently wandering around scaring the living daylights out of everyone, nobody except for Mr. Bradley seems to be willing to do something about it.
Jimmy looks nothing like his parents (yes, he and his father have blue eyes but Jimmy's are almost violet) so he could have been adopted or one of his parents is his step-parent.
- My guess would be that his mother is actually his step-mother (and Jimmy thus takes after his biological mother). The earlier episodes featuring Jimmy never showed or mentioned her, so it's possible she and Jimmy's dad got into a relationship during the later half of season 1.
The Normans, like the Jennifers, have the same name but look nothing alike and love to bully Casper's best friend.
He is the only main antagonist to not have been this for a whole season.