What do Ernest Borgnine, Tom Skerrit, William Shatner, Anton LaVey, and John Travolta have in common?
A little picture called "Devil's Rain."

The 1970s were a good time for Satan. He had a shitpile of movies - some good, some truly awful - all made about him. Guess which category this one falls into?
The plot (er) is basically this: a bunch of Satanist pilgrims somehow live some fucked-up half life in a town in the middle of nowhere. Shatner's family are their enemies, and most of them wind up melting into puddles of bubbling tempra paint. There's something about a book that Borgnine, leader of the Satanists, needs, and a bunch of people wind up trapped in what looks like a portable fireplace.
Shatner is in full, well, Shatner-mode through this one, and Borgine's eyebrows are the scariest thing you'll ever see. You also get to see, quite clearly, how the Michael Myers mask came to be once Shatty's eyeballs are turned into blank and staring sockets.
LaVey was the technical advisor, which made me choke on my drink as the beginning credits rolled by.
Watch it on YouTube!