Here is some cool concept art by Kevin Eastman for the fourth live-action Turtles movie that never was. Eastman did the art from 1995 to 1997 for the film tentatively titled, TMNT: The Next Mutation. The images show off the "fifth turtle" Kirby, as well as Fang, Shredder, Spyder, Nano Spyder, Super Shredder, Kasey (Casey), Talbot, Lawson, Bugman, and Evil April.
The fourth fillm was planned as being less kid-friendly, which would have been cool. Check out the art thanks to CBM and share your thoughts in the comments.