Moby Dick and the Mighty Mightor

The Electrifying Shoctopus [Moby Dick] (1x29)

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Tom has Moby take him Tubb and Scooby to an old pirate ship that he discovered on the ocean floor. The boys go inside the ship and find a secret compartment in the Captain's quarters with a treasure map inside. They hear a noise and see the Electrifying Shoctopus: an octopus-shaped underwater craft piloted by Captain Squid. Captain Squid captures the boys and takes their newly found treasure map.