While helping renowned oceanographer Professor Poisson research the sunken pirate ship Diablo Doro, the gang encounters the ship's captain Pescado and his crew of sea monsters, the Octopus Monster and the Kelp Monster, who kidnap the professor in order to stop his research. The gang must rescue him as a result.
This episode includes examples of the following:
- Botanical Abomination: One of the villains is the Kelp Monster, a humanoid monster made up out of seaweed.
- Ghost Pirate: The episode's main villain is disguised as Captain Pescado, a ghostly pirate.
- "Scooby-Doo" Hoax: The villains are out to steal treasure from the sunken Diablo Doro, and use their monster suits to scare away intruders.
- Screw This, I'm Outta Here: The three crewmen of the Sea Prowler announce their intention to head back to shore in the launch to get away from the monsters and Shaggy and Scooby very nearly accompany them. Of course, since those three crewmen are the culprits, they were staging the whole thing.
- Tentacled Terror: One of the villains is an octopus with human-esque legs and a mouth in the wrong place.
