The Incubus

Incubus is a 1981 Canadian supernatural slasher film directed by John Hough and starring John Cassavetes, Kerrie Keane, and John Ireland. The plot focuses on a small Wisconsin town where a mysterious figure is raping and murdering young women. It is based on the 1976 novel of the same name by Ray Russell. The screenplay for the film was originally completed by Sandor Stern, though it was so significantly rewritten by star Cassavetes during production that a pseudonymous "George Franklin" received the official credit as screenwriter.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.