Jerkass Woobie: Farquard the butler. He's fairly unpleasant to the Scooby gang, shows no concern for their well being, and seems just a bit unhinged. Still, if you served someone for more than 60 years and your reward was to continue your service, this time to someone you've never even met, you'd probably be hacked off a bit too.
Rescued from the Scrappy Heap: Scrappy-Doo is a bit more bearable in this movie, since he's needed to solve the riddles until Shaggy gets enough of a clear head to figure out the last few. Also in the opening, when he heard about ghosts, Scrappy's first thought isn't to fight them, but that ghosts are neat. The two people he seriously confronts in the movie are the butler and the gorilla, neither of whom was a person in a costume anyway.
This part of his characterization comes from earlier. In the two 4-person gang runs Scrappy was often paired with Daphne as the gang's new clue solver, to Daphne's new found leadership and no more damsel mode. Allowing Scoob and Shag to do their thing without having to include Scrappy in their interactions.
He also saves Shaggy and Scooby by tricking Billy Bob into getting chased away by a bear.
And Scrappy is the first to think that maybe the escaped ape isn't vicious, but lost and scared. He's right.
Still the devout Scrappy haters will say he gets annoying at times the way Scrappy solves all the clues.