The IMDB says eight movies have been made bearing the title Incubus. I rented the first one, released in 1965. It stars a pre-Kirk William Shatner, who plays a soldier returning home from a war, and right away there's trouble. He tries to protect his sister from an incubus while at the same time dealing with a succubus who has targeted him. If that isn't weird enough, here's the kicker: all the dialogue is in Esperanto.
Written and directed by Leslie Stevens, produced by Anthony A. Taylor, with a score by Dominic Frontiere and starkly beautiful photograpy by Conrad Hall. Shatner, Stevens, Taylor, Frontiere, Hall -- the one thing those five men had in common was The Outer Limits. Can't you just see them sitting around on a soundstage, waiting for the next scene to be set up, and one of them says, "Hey, kids! Let's do an Esperanto movie!"
Recommended only as a curiosity.