Heathcliff and the Catillac Cats

Monstro vs. the Wolf Hound [Catillac Cats] (1x22)

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Riff Raff and the cats watch a horror movie, and that night Riff Raff dreams he is Dr. Frankencat and has created a monster. It's a regular nightmare, with even Leroy showing up as the Wolfman. Riff Raff wakes up screaming for help, and glad it was all a dream.