A Night of Fright is No Delight - S1-E16
Continuity mistake: When the goldfish snaps at Shaggy for taking his fish food, there are some rocks at the bottom of the bowl, but when Shaggy says "Sorry" and puts the box down, the rocks have disappeared.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When Fred is reading his book in bed, he is wearing his pyjamas, but when Fred says "You got to be kidding", he is wearing his regular clothes, and when he, Scooby and Shaggy go back into the bathroom to inspect the bathtub, Fred is back in his pyjamas again.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When the gang peek out of their rooms after hearing spooky noises from Cousin Simple's room, Fred is wearing his regular clothes, but in the next shot he is wearing his pyjamas.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When Shaggy notices footprints in the ground in the cave, he is standing behind Velma, but in a close-up of Velma in the next shot, Shaggy has gone.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When Velma tells Shaggy that they are going to follow the Phantom Shadow's footprints, her glasses have no lenses in them, but they re-appear in the next shot.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When the flying uniform chases Scooby, Shaggy and Velma, the shoulder strap changes shoulder whenever the uniform changes direction.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When Scooby, Shaggy and Velma go up the elevator, Velma operates it with a hand lever, but when they arrive at Cousin Slicker's room, the lever has gone.
A Night of Fright is No Delight - S1-E16
Continuity mistake: When the gang meet up and realise that all the heirs are missing, Daphne is behind Scooby, but in a close-up of Scooby in the next shot, she has disappeared.
Continuity mistake: The Snow Ghost's mask goes from being a hood type to just covering the guy's face in one shot when he's stuck in the snow.
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.