Even More Heroes In A Half-Shell From The TMNT Movie Makeover That Didn't Happen

Haha, this stuff. I've seen them before.

So the mutants keep mutating. This was for the fourth movie subtitled "The Next Mutation." As Mark Pellegrini says below, that title was re-used for the live-action TV show (where it didn't make sense because the idea of further mutations was dropped). The Hulk/monster transformations was used at the end of the original cartoon series, as well as for Raphael when Peter Laird got back to writing comics.

Here are the mutations: Raphael and Splinter would be monsters (guys at Mirage admitted they used the same idea twice). Leonardo would be Colossus from X-Men, turning his skin into a hard material. Michelangelo had the mental ability to trick people into seeing him as a human, though he had to wear clothes otherwise they'd see him as a naked human! Donatello gained straight-up psychic powers, but was nearly blind.

this is for the the next mutation not a unmade fourth live-action