Screamers (1981, but really 1979 & 1980)
People are terrorized by men turned inside out...or it's a movie about fish people getting treasure from Atlantis. Yes, definitely the latter.
Well, to be fair, the story behind Screamers is more interesting than the movie (which is fun in its own way). See, in 1979, the movie Island of the Fishmen was released in Italy. This 95 minute movie was given over to Roger Corman to distribute in the U.S. Corman being Corman, he thought the movie was too slow, lacking in gore, and needed some help being successful. So, he cut out about half an hour for pacing, recorded twelve new minutes of footage (including our favorite Space Santa, Cameron Mitchell) as a prologue as well as some different "transitional fishman" footage towards the end, and called it Something Waits in the Dark.
It didn't do well. So, about a year later, Corman retitled the movie Screamers, created a poster about people being turned inside out, and had a protege of his film a trailer with footage that never appears in the film to get people interested.
In other words, Screamers' poster, trailer, and premise are a complete lie about the actual movie, to the point that for the theatrical run, Corman spliced in the fake trailer footage clumsily to all the theatrical prints just so people wouldn't demand their money back.
Sad thing is, the Screamers movie as shown in the trailer (it's on YouTube) probably would have been a lot of fun, but the movie we have is just a cropped down, slightly gorier version of a movie that is fairly watchable. Sure, the Fishmen are clearly rubber suits, but the movie itself is just fine, as long as you enjoy 70s Italian B-Movies.