Both characters were pretty sinister and interesting to say the least. I think they could have carried a plot about the black mass etc. A spin-off prequel to taste..
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I agree with you and would definitely watch that movie if it existed. Lord Courtley was so evil, I could've easily seen him as the villain in his own horror movie. He was so creepy we almost didn't need Dracula (but I'm glad he was there because how could anyone possibly complain about Christopher Lee starring in a movie?) Courtley actually reminded me of Aristede from Dark Shadows for some odd reason.
Death lives in the Vault of Horror!