Continuity mistake: When Scooby is looking for the rabbit in the magician's hat, the position of Scooby's fingers on the rim of the hat change between shots.
Other mistake: When Fred hears footsteps, he says "Into the closet." But the closet has stairs and passageways inside.
Continuity mistake: Scooby uses a magic wand to produce some flowers from the magician's hat, and he is holding the wand in his right hand when the flowers appear. When he is soaked by the flowers, he raises his right hand but the wand is nowhere to be seen.
Continuity mistake: When Fred says "We've lost him", Shaggy says "Groovy." His eyes then disappear.
Continuity mistake: When Scooby lands on the Phantom, the Phantom has nothing on his hands. When we see him talking to Fred a little later on, he is now wearing green gloves.
Continuity mistake: When Scooby lands on the Phantom, the gang cheer and Daphne and Velma are between Fred and Shaggy. In the next shot, we see Daphne and Velma, but Fred and Shaggy have disappeared.
Other mistake: When Shaggy is on the ground after being struck on the head by a vase, the inside of Scooby's eyes are brown instead of white.
Continuity mistake: When Daphne picks up the large key, there is a chest of drawers behind her that disappears when we see a close-up of the key.
Other mistake: When the gang are reading the book in the library, the page they are on says "2", despite the fact that they are halfway through the book.
Continuity mistake: When the gang are walking along in the castle, in a close-up of Velma and Daphne walking in the background a knight's armour and a shield, but when Daphne falls through the trap door, both the armour and shield disappear.
Continuity mistake: When Fred, Velma, Shaggy and Scooby discover that Daphne has fallen through the trap door, look at Shaggy and there is nothing on the wall, but when we see Shaggy scared by the ghost, a shield has suddenly appeared.
Continuity mistake: When the ham sandwich floats down in front of Shaggy, the sandwich has lettuce in the middle. When we see the sandwich on the table, the lettuce has gone.
Continuity mistake: After Scooby reads "Danger - Leave Haunted Isle" on the back of the map which Fred is looking at, he turns the map around and on the front there is an outline of an island. In the next shot, the outline has disappeared.
Continuity mistake: When Daphne is holding the large key, the rims on her cuffs are violet, but in a close-up, they are white.
Continuity mistake: When Fred is holding the map that Scooby found, he is initially looking at the back, but in the next shot, it has suddenly turned correctly.
Continuity mistake: In a close-up of Scooby and Velma on the boat, the spots on Scooby's back are missing.
Continuity mistake: When we first see a close-up of the gang on the boat, the pleats on Velma's skirt are missing.
Chosen answer: A ghost wouldn't have to keep any food in the fridge - they don't need to eat. So it is one thing that proves the ghost is not a ghost.