Moby Dick and the Mighty Mightor

The Sinister Sea Saucer [Moby Dick] (1x23)

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Tom, Tubb and Scooby are water skiing behind their friend Moby when they notice what looks like a space capsule about to splash down in the ocean. Manta Menace is waiting for the capsule and its contents: the secret maps of the Mars diamond mines. The boys see the capsule sink and have Moby take them in so they can investigate.