The Harum-Scarum Sanitarium - S1-E11
Continuity mistake: Shaggy goes back and forth from being in the front seat to the back seat of the Mystery Machine as the episode starts.
The Ghost of The Bad Humor Man - S1-E4
Continuity mistake: The back doors of the armored truck that the phantoms are trapped in go from being open to closed to open again.
The Harum-Scarum Sanitarium - S1-E11
Continuity mistake: Fred and Velma get chased by one of the dogs into the room where Shaggy and Scooby are. Daphne wasn't with either pair, yet she's suddenly there once Fred closes the door.