Incubus

Kia is a succubus, luring to their final perdition men who already have sinful habits and libertine inclinations. She tires of this, it's too easy, and these souls are going to Hell anyway. She wants to match wits and charm with someone who is good. So, against the advice of her sister Amael, Kia seeks out Marc, a man who has already faced death with courage. After a night together, Kia finds that not only is Marc's goodness still intact, but she has been ravaged by love. In anger, she and Amael conjure an incubus to deal with Marc. The incubus starts with Marc's sister, Arndis. Who will win the struggle for souls? from IMDb

Here is a surprisingly gripping and intense horror film complete with succubi, a young William Shatner, and high contrast expressionist photography. It was made by a shoot off crew from the Outer Limits team, directed by Leslie Stevens, and filmed by 3 time Oscar winner Conrad Hall(American Beauty, Butch Cassidy and the Sundance Kid, and Road to Perdition).

Unlike the usual horror film, and more akin to the films of Bergman, Incubus is very poetic in its storytelling. The stylistic filmmaking relies heavily on symbolic conventions that bolster the struggle between good and evil.

The dialogue is entirely in esperanto which makes Incubus seem like a film from an imaginary european culture. There are imbedded english subtitles with this file. Unfortunately they ride really high on the screen, sometimes blocking important parts of the shot, but this doesn't spoil the experience too much, and is currently the only way to see the film.

From ArtsEditor.com on the mythology of the film:

Incubus is a chilling black and white American film from 1965 that tells a timeless tale of good vs. evil. It features as its star William Shatner. The film has remained somewhat of a footnote for many years, largely because it was taken out of distribution when two of the actors died within a year of the film's release. Fearing a purported curse" on the film, the director ordered all prints withdrawn, and Incubus subsequently remained "lost" for over 30 years. Until now, as they say. Incubus has been "found," restored, and released on home video with English subtitles."