The Dunwich Horror (1970)

There's something wrong with the Whateley boy. This 1970 adaptation of the Dunwich Horror was produced by Roger Corman, which should say everything you need to know. It's a very loose treatment of the short story, which is mostly a history of the Whateley family with a big ol' monster battled added onto the end. The movie, instead, makes the story about seduction and abduction, but the plan remains: summon Yog-Sothoth at all costs.