In 1996 the popularity of the Teenage Mutant Ninja Turtle franchise was worldwide, including Japan, where talking green monsters are the norm. TMNT was wildly successful, and the toy company Takara wanted to capitalize further. So two new, Japan-only Original Video Animation specials were produced for specific toy lines, giving fans Mutant Turtles: 
The first OVA was called “The Great Crisis of the Super Turtles! The Saint Appears!”, and showcased the Supermutant toy line. The back-story for the episode involves the Turtles and Splinter meeting a little fairy named Crys-Mu, who gives them the Muta-Stone. Using its power allowed everyone’s favorite (and clearly, by Japanese standards, average) teenage ninjas to change into super mutants, taking on human-like forms with enhanced fighting prowess and weapons. Shredder, Bebop, and Rocksteady had their own Dark Muta-Stone, and also became super mutants (with Shredder transforming into a dragon).
When the Turtles needed extra power, all four combined their super mutant forms and became Turtle Saint, which they used to fight off Dark-Mu – Crys-Mu’s antithesis. In the end, Turtle Saint uses all his power to seal away Dark-Mu, returning the Turtles to their average, mundane mutant forms forever. (Or, at least until the second OVA!)
OVA episodes are a lot of fun. They show up in anime series all the time as a way to see characters in out-of-their-ordinary situations. Beyond that, this particular OVA served another purpose, while still attempting to maintain a 
There are also problems with doing this sort of additional episode. First was the animation; the animators were painstakingly matching the cartoon’s style whenever needed, especially the way the Turtles were drawn. But it wasn’t always successful, and there was likely a sigh of relief when the super mutants showed up halfway through and everything could adopt a more classic anime look. Second, the episode was almost too ludicrous. It’s hard to argue that the 1987 animated show wasn’t ridiculous 95% of the time. It couldn’t take itself too seriously, because the nature of the program. But even in the same context as that series, this particular episode was a bit much. Shredder, Krang, and even the Turtles themselves were bumbling idiots for most of it. The only competent ones were Splinter and Turtle Saint. That’s fine and well, but the characters developed over ten years didn’t have to be ditched just to sell one toy, especially when the OVA had at least 8-9 minutes more run time to flesh out the story.
