Frankly, it's not hard to see the similarities between the two, between Rosemary's Baby and The Mephisto Waltz, or at least the imprint of one on the other. We've got this educated passing for sophisticated, sufficiently urbane couple, and they're drawn in by a pair of Satanists of indeterminate age, and then they get involved in magic that benefits the Satanists more than the sweet young couple. So it's a little bit Faustian, but it's got jazz hands.