What a Night for a Knight - S1-E1
Plot hole: It seems unlikely that: 1. The curator, who's short and chubby could fit into that suit of armor. 2. How he could be strong enough to lift up the table Scooby and Shaggy are hiding under at one point, 3. That the museum has no security guards who might catch the curator and his thugs during their art forgery scheme and 4. There are eyes shown moving in the suit of armor when the gang's talking to the curator despite the fact he's the Black Knight Ghost.
What a Night for a Knight - S1-E1
Continuity mistake: Scooby's carrying the left shoe of the missing Professor White yet when they find him he's missing his right shoe.
What a Night for a Knight - S1-E1
Continuity mistake: When Daphne suggests leaving the painting room through another door, the Black Knight appears and you can see he has red crest of hair on his helmet. But after a quick cut, we return to the gang and the crest on his helmet is missing. It re-appears when he comes to the painting that Shaggy is hiding behind.
What a Night for a Knight - S1-E1
Continuity mistake: When Scooby sees the Black Knight, he throws up the bones and they form a skeleton of a dinosaur. When we see a close-up of Scooby in the next shot, the dinosaur skeleton is nowhere to be seen.
What a Night for a Knight - S1-E1
Continuity mistake: When Velma loses her glasses, the Black Knight trips over her and lands on the guillotine. She mistakes the Black Knight's growls for Shaggy's sore throat, and pours some cough mixture on to a spoon. When Shaggy enters and runs up to Velma, she is wearing her glasses again.
What a Night for a Knight - S1-E1
Continuity mistake: When Velma says "What a spooky place!" to Scooby, you can see Velma is standing by Scooby but in the next shot she has disappeared.
What a Night for a Knight - S1-E1
Continuity mistake: When Scooby is guarding the door, it is open. When he stops, it is open, and in the shot after that, the door is closed again.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang arrive at the Museum, you can see the handle on the Rear Entrance door is on the left hand side. When Shaggy opens the door and lets Fred, Daphne and Velma in, the handle is now on the right.
What a Night for a Knight - S1-E1
Continuity mistake: When Shaggy puts the ladder on the wall near the Museum Rear Entrance, you can Fred is standing by an open door of the Mystery Machine. In the next shot, he is now standing near Shaggy.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang say "Professor Hyde White!" in the library, you can see Shaggy has his hand on Fred's shoulder. When we Fred and Velma in the next shot, he doesn't.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang are driving along in the Mystery Machine, you can see Velma is sitting by the window. When we see a full view of the front seat, she is now sitting between Shaggy and Daphne.
What a Night for a Knight - S1-E1
Continuity mistake: When Mr Wickles is standing by the crate containing the Black Knight armour, you can see the lid is resting on it. But in a close-up of Mr Wickles, the lid is missing.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang discover an empty suit of Black Knight armour in the truck, you can see the helmet is beside the wheel. When Daphne notices a piece of paper by the wheel, the helmet is nowhere to be seen.
What a Night for a Knight - S1-E1
Continuity mistake: When we see the truck at the beginning of the episode, you can see that the label on the crate is completely clear. When the Black Knight opens the crate, the label now has writing on it.
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.