Star Trek: Planet of the Titans

Star Trek: Planet of the Titans is another early version of Star Trek: The Motion Picture

Plot
The film would have involved the crew of the Enterprise accidentally went back to the prehistoric era, where the crew possess powers (like Kirk having the ability to breathe fire). Only to discover that they are the Titans.

Why It Was Cancelled

 * 1) The executives rejected the idea.
 * 2) Ideas for a Star Trek movie were cancelled in favor to bring the series back to the small screen with Star Trek: Phase II. Though the latter half was cancelled due to the success of Star Wars, and the decision was made to turn the 2 hour pilot episode into a full length movie.

Result

 * Star Trek: Planet of the Titans was permanently cancelled.
 * Elements were used in Star Trek: The Motion Picture''.