The story is that while filming Flesh for Frankenstein Paul Morrissey and crew discovered they were quite ahead of schedule and under budget, so they decided to make a second movie. Released the following year, Blood for Dracula, which shares Frankenstein's critique of sexual promiscuity, was partially improvised and for some reason has a cameo from Roman Polanski. It's also a much more entertaining movie no matter what the Rotten Tomato ratings suggest, despite Joe Dallesandro's character being much more overbearing and hard to handle.
Paul Morrissey's 1973 horror-comedy was originally titled Andy Warhol's Frankenstein despite the fact that Andy Warhol had virtually nothing to do with it. Udo Kier (whose name is amazing) stars as the good doctor in this bizarrely sexualized telling of Mary Shelley's classic that doubles as a critique of Free Love. In 3D! (Where available.) It was originally rated X for all the sex and gore, almost rivaling Salo on that front, though playing it for comedy makes it quite a bit more palatable. Also, as if anything could even come close to rivaling Salo on that front.