The Octopus Monster was the sea monster disguise of Mr. McGil.
The Octopus Monster has an octopus head with a mouth full of sharp teeth, big eye brows, blue scales, four tentacles, and legs with webbed feet.
The Octopus Monster a very cruel monster when helping the Ghost of Captain Pescado and the Kelp Monster trapping Velma Dinkley, Fred Jones, and Daphne Blake. The Octopus Monster seems to be hungry when he took Shaggy Rogers and Scooby-Doo's breakfast at the galley.
The Scooby-Doo Show
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 and Scooby 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 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 and Daphne. The Octopus Monster was captured with Captain Pescado and the Kelp Monster. (Scooby-Doo, Where's the Crew?)
- It was referred to by name once, by Shaggy.