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 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: 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.