The Octopus Monster was the disguise of Mr. McGil.
He was voiced by the late Casey Kasem.
The Octopus Monster came out of the water and entered the ship with the Ghost of Captain Pescado and the Kelp Monster. He chased Shaggy Rogers and Scooby-Doo into the galley and locked them in the door. Shaggy cooked greasy pancakes and Scooby left them on the table without watching the window when the Octopus Monster stole all the pancakes and ate them. Shaggy thought Scooby ate all the pancakes, but he saw the milk, syrup, and butter taken by the Octopus Monster and the vicious sea monster consume them and Shaggy realized he was cooking breakfast for a hungry sea monster. While Scoob and Shag were tip toeing, they saw a shadow and thought it was the Octopus Monster, but it was just Fred Jones and Daphne Blake. The Octopus Monster was captured with Captain Pescado and the Kelp Monster.