Scooby-Doo and Scrappy-Doo (1979)

The Scarab Lives! - S1-E1

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.

Dan Moat

Twenty Thousand Screams Under the Sea - S1-E9

Plot hole: During the diving contest Tiger Morris, who's posing as the sea monster, fakes his cries of terror and flees off to the left of the ocean. Then, seconds later he's suddenly back as the sea monster. Impossible for him to get into disguise that quickly.

Rob245