TMNT: The Next Mutation

TMNT: The Next Mutation was a planned sequel in the original Teenage Mutant Ninja Turtles film series. It was intended to have the Ninja Turtles and Splinter undergo unstable mutations.

The project saw work beginning in 1994.

Plot
Splinter and the Ninja Turtles undergo mutations.

Why It Was Cancelled

 * 1) The cancellation reasons are currently unknown, but it's most likely due to the failure of the third film.

Result

 * The original live-action series from the early '90s has three films.
 * The idea of the Ninja Turtles and Splinter undergoing unstable mutations ended up as a plot during season 9 of the 1987—1996 animated television series.