Plot hole: There is a "scarab alarm" when the blue scarab arrives, Shaggy even comments on hearing this. The problem is, The Blue Scarab is a comic book, so the villain and Shaggy wouldn't know what the Scarab alarm sounded like.
Other mistake: When Scooby is eating the hot dogs at the "Hotus Dogus" stand, his tail goes transparent.
Continuity mistake: When Scooby and Shaggy are at the "Hotus Dogus" stand in the Coliseum, you can see that Scooby has two flags in his left hand, but after a quick close-up of Scooby, we return to him and his flags have disappeared.
