Even though Shaggy is a contestant on a game show, he can clearly be seen cheering in the crowd when they cut to the audience.
Prestina's outfit changes colors between shots, making her pants look like her shirt is actually a leotard.
When Freddy confronts The Great Mel, Mel's arm is used to poke Mel instead of Fred's.
Al Cabone's mouth doesn't move when he says "Blah, see? Blah!" after Scooby baits him out.