WMG / Casper

Casper (from the early 1990s movie) is Charles Foster Kane.
The poor, rural background of Kane's family is a cover. The "hick" father is actually a loving Mad Scientist. The reason Kane's mother wants to send him away is that she doesn't approve of her husband's experiments, and dosen't want to her son to get into them. The father, depressed and enraged, plunges into his work...

According to some paranormal researchers (or so I've heard), people's spirits can leave (again, this is a movie, so screw physics I have plot), residual energy behind. Kane's father became obsessed with harnassing this energy that Kane would have left at his home with Rosebud. It works (somewhat) creating Casper, the friendly ghost and essence of Charles Foster Kane's happiness.

Anyway, I think this is what I heard paranormal researchers believe (though I don't myself). If anyone knows anything else about this, feel free to fix any mistakes in understanding I have shown.
  • Kane's parents lived in Colorado, Xanadu is in Florida and Whipstaff Manor is in Maine. That looks like a bit of a geography problem.

Ray had a good reason to bail on the job.
It was one against three. Furthermore, wrangling ghosts with a proton stream and throwing a trap is probably a pretty hard job for just one person. Still, it was kind of stupid for him to go in alone.
  • Maybe the ghosts were simultaneously too much of a threat for one, but not big enough to call in the whole group when they had bigger fish to fry. Or maybe she did make another appointment for all four, but they were so backed up that she couldn't see them for a while.
  • Maybe he just couldn't bust Casper's uncles in front of him because he had the same standards the Bride had, and he couldn't bust Casper himself because he was a child.
  • If you look carefully when Ray runs out of the manor, the emitter on his Nutrona Wand has come away from the rest of it and is hanging on its wire. Might be a little dangerous to use it again...

The Ghostly Trio are another reason Casper's father invented the resurrector
Think about it - John McFadden's brothers all die violent and/or painful deaths. Then Casper dies of pneumonia. No wonder McFadden wanted to make a machine to bring people back from the dead. I couldn't help but wonder what their unfinished business was. Casper's was looking after his dad.
  • Maybe their unfinished business was looking after Casper and his dad? They seemed to have a soft spot for Casper. If they were close, they might have stuck around to watch over Casper while his dad was likely depressed over their deaths.
  • How do we know that they're not Casper's mom's brothers?
    • We don't, but that doesn't mean Casper's father wouldn't want to bring them back, if they were friends.
    • They use the surname McFadden in the cartoon.

Peter Venkman refused the job because Carrigan couldn't afford a down payment
Peter got screwed so many times with unpaid jobs he now demands advanced payments and wouldn't believe Carrigan when she offers a share of the treasure.

Carrigan is related to Casper.
Her father wasn't just some rich guy who foolishly invested in the creepy place before leaving it to her, it's in the family, and has been passed down through generations. Based on what we see of Casper in his human form, there is family resemblance.

Ghosts look more cartoonish over time.
Notice Kat's dad and Carrigan looked more or less like themselves in ghost form, whereas Casper and the trio look like cartoonish beings and barely resemble humans anymore. Kat's dad and Carrigan spent a couple hours as ghosts whereas Casper and the trio have been that way nearly a century (Casper died in early 1900s IIRC).

The movie is taken place in the same universe as Ghostbusters.
Around some time after the events of the first movie and before the events of the second movie. The Ghostbusters were all but broken up and Ray was the only one available.
  • Or the movie takes place around the time it was made, and the events of Ghostbusters I and II (and maybe the cartoon) already happened. The Ghostbusters were busy with an unseen case, and had only one of them go to deal with the Ghostly Trio.

Carrigan went straight to Hell when she crossed over
Just to make her defeat that much more awesome, she'll be facing an eternity of karma in the afterlife...