Dark Shadows version
Has anyone seen the "Leviathan" storyline on Dark Shadows, which borrowed from The Dunwich Horror?
Unfortunately, it didn't go so well and the writers retconned the origin 3/4 of the way through and then it fell apart all together.
They actually started to introduce the next storyline 2 1/2 weeks before this one ended with both stories occupying 1/2 of the episode.