The Aaron Sims Company, the design studio that has worked on films such as Dawn of the Planet of the Apes, Green Lantern, and, more recently, Teenage Mutant Ninja Turtles, has released some concept art from TMNT that shows a handful characters that never made it into the actual movie (via Screen Crush). The concept art features three staples from the 1980-90s Teenage Mutant Ninja Turtles cartoon series: Bebop, Rocksteady, and Krang. These character, created specifically for the animated series in order to provide more characters for Playmates to make toys out of, have never been translated to film. Some fans held out hope of seeing them in the latest Turtles film, but it wasn’t to be. The concept art suggests that they were part of the script at some point in the process.
For those unaware, Bebop and Rocksteady were two thugs that Shredder turned into mutant henchmen to help him fight the Turtles. Krang is an alien from Dimension X who teamed up with Shredder to try to take over the world.