The Kelp Monster was the disguise of Mr. McFinn.
The Kelp Monster is a big glowing green seaweed creature with eye holes, a mouth hole, legs, and arms.
The Scooby-Doo Show
The Kelp Monster attacked the gang alongside the Ghost of Captain Pescado and the Octopus Monster. He was sleeping in the control center, until the Octopus Monster chased Shaggy Rogers and Scooby-Doo and the Kelp Monster woke up and chased Velma Dinkley. The Kelp Monster and his pals found Scooby, Shaggy, and Velma in a sunken ship. The three ghosts were captured. Pescado was First Mate Carp, Kelp Monster was McFinn, and the Octopus Monster was Mr. McGil. The three criminals were taken to jail.
- Its name is spoken once, by Velma.
- In Scooby-Doo! And The Goblin King, the Kelp Monster was among the monsters seen in the monster bar.