It was dressed in a smoking jacket and recognized a Beauregard heirloom. I suppose they were intending to be a ghost of someone gentile who used to know the Beauregards.
What happened to Billy Bob?
It's possible that he gave up due to being too injured after falling off the cliff, or having run out of rifles.
What caused Shaggy's pants to move?
Presumably either hidden wires or a real ghost.
Who set Shaggy's truck to sink?
This one is unresolved because it isn't clear if someone did sabotage the truck (in which case it would probably have been the Sheriff) or if the truck sunk by pure accident and the Sheriff found it and put it to use when he was running through the caves and secret passages. Then again it might also be possible the "mud trap" is actually a deliberate security feature no one else knew about? Uncle Beauregard's mansion was full of them, having one on the outside to make a vehicle disappear (especially when you have hillbilly neighbors trying to shoot up your property) might be a useful tool.
How did the sheriff disguise his fatness while in his various disguises? Did we wear a corset as the ghosts? Was he never that fat to begin with and just wearing a fake stomach to more closely resemble his brother?
The Skull Ghost costume still reveals his fatness, and has black outlines in contradiction of the first skull ghost who is just bones. The Colonel is wearing rather baggy clothes and does appear he may have been a bit husky in life so not a big deal.
Why did Shaggy and Scooby never try to keep the ghost of the Colonel from attacking them by stating that Shaggy was his nephew and the person he'd actually left his fortune to?
This is a fair question although given Shaggy is a coward and from the minute they got there said ghost has been yelling for him to "leave this place" Maybe he thinks his Uncle changed his mind. Can't exactly update your will after you die.....right?
Who was that at the beginning of the movie? The poor old witch seems to have no relevance at all to the plot.
What happened to the roof of Shaggy's truck? Before it sinks in the mud, it has a roof. But after they find it in the cave, the truck is roofless. Did the truck lose its roof while sinking? Or did the Skull Ghost remove it for a better signal for his remote control?
The Boo Brothers, bored of doing nothing (in their own movie), invite a bunch of ghosts to the Mansion to have a party. In their own words those ghosts are 'their family'. However when the Party is over and Shaggy threatens to kick the Boo Brothers out, they claim they are orphans. What gives?
Probably to gain sympathy or the other ghosts weren't literally their family, just people they call their "family".
How do Billy Bob and Farquaad not recognize that the sheriff is a fake? They've lived there a long time and should easily notice if there is a sudden change like that.
Well the Fake Sheriff turned out to be Sheriff Rufus Buzby's twin brother T.J. Buzby, and, besides slight differences in their voices, the only difference between them is the fact that Rufus has a large handlebar mustache. They probably just assumed he shaved it.
