Continuity mistake: To catch Ripley, Fred uses the remote to bring the draw bridge up. But Ripley manages to scale the bridge before it gets all the way up and falls into the moat below. As he surfaces, the draw bridge is instantly and suddenly down all the way again as the gang rush out onto it.
Continuity mistake: Sledding down the stairs on a shield, Velma, Shaggy, and Scooby are trying to escape the dragon hot on their tails. Velma grabs a spear from a coat of arms on the wall, but when the shot cuts back to her about to shove it in the dragon's mouth, the coat of arms vanishes when they were just passing by it.
Continuity mistake: After Daphne touches the dragon's tail, Shaggy and Scooby take off and run into one of those coffin like things with spikes on the inside for torture, to hide. As they go in, you can see the spikes on both sides, and there is nothing else in it. But when Shaggy turns on a flashlight, you can see the spikes to their back have vanished, and a skeleton appears.
Continuity mistake: When Fred walks up to Excalibur, the design is different than when seen later after Shaggy and Scooby are scared by the dragon. The blade has designs on it, including a gold and green diamond shape, and the hand guard is curved. And the handle is wavy, with the end of it being a gray cone shape. Then after Scooby and Shaggy come running, it is shown again. Only now the shape of the blade is different, the gold and green diamond part have vanished, the hand guard is now just straight, the handle is not wavy, and the gray cone at the end has turned into a sphere.
Continuity mistake: After the people start running away when the dragon arrives, Shaggy and Scooby are shown still locked up and the food splatters on their holders are there. A couple shots later, the food splats change around in position and color. And then moments later, the food vanishes from the wood all together.
Continuity mistake: As Scooby and Shaggy are locked up for stealing the frozen bananas, the lock is placed on their holder hanging down straight. A couple shots later, it is now hanging out to the side and is smaller, most noticeably the lock hole is smaller. The lock hole also changes what side it is on.
Continuity mistake: Velma and Daphne are sitting on a bench, with Velma on the left and Daphne on the right. When they hear Shaggy and Scooby screaming they quickly stand up and the shot changes to show them running past the girls. The bench they were sitting on vanishes, and the girls switch places.
Continuity mistake: As Shaggy is handing Scooby a tower of food, he has one hand on each tower at the bottom, and Scooby reaches out with just one paw to take it while Shaggy is speaking. Before Shaggy finishes his sentence, it cuts to a close up while Scooby is touching his tower, and suddenly Shaggy is only holding his tower with a hand on bottom and top, and Scooby is suddenly doing the same with his.
Continuity mistake: As the gang are walking through a market like area, Shaggy says "Like, I can't believe we came all the way to Scotland for a renaissance fair." As he does, the shot changes and suddenly he, Fred, Scooby, and Daphne are looking to their right, when they were all looking straight in the previous shot. The group's arrangement also changes from more scattered, to being in basically a straight line side to side.