4. Monster a Go-Go (1965)
Directors: Bill Rebane and Herschell Gordon Lewis
Stars: Phil Morton, June Travis, George Perry, Lois Brooks, Peter Thompson
Monster a Go-Go's production history is almost funnier than the film's goofy title. Original director Bill Rebane proved unable to finish shooting once he and his team ran out of money in 1961. Four years later, schlock master Herschel Gordon Lewis stepped in and, using different actors, filmed more scenes.
Thus, characters' appearances change throughout the course of the film, and, best of all, Lewis' inability to shoot additional scenes with the eponymous astronaut-turned-creature led to him closing Monster a Go-Go with a long, lame-brained bit of narration that convolutedly explains how the monster was never there to begin with: "The line between science fiction and science fact is microscopically thin! You have witnessed the line being shaved even thinner! But is the menace with us? Or is the monster gone?" And, lastly, are you fucking kidding us?