Batman is the dark knight, Teenage Mutant Ninja Turtles are crimefighting mutants. The two teaming up shouldn’t work on paper, but it totally does when you see it animated.
We always love when superheroes team up, just look at Avengers or Justice League. Unfortunately, we will probably never see Superman team up with Iron Man or Captain Marvel team up with Shazam (high five if you got that) because Marvel is a direct competitor to DC. The Teenage Mutant Ninja Turtles aren’t tied to those bonds, so they can literally bounce in and out whichever universe they want. Their origins are closely tied with Marvel (the ooze that made Daredevil blind is the one that mutated them into the TMNT.
Or when TMNT’s Shredder teams up with Batman’s Ra’s Al Ghul (among other villains) the turtles can jump into the Gotham and try to defeat them. Unfortunately, Batman only sees mutant turtles and thinks they’re the enemies. The two fight, one of them mention Martha and they realize that they aren’t the true enemy (I’m only half joking about that I hope).
Batman vs. Teenage Mutant Ninja Turtles’ releases on Digital May 14, 2019, and on 4K Ultra HD and Blu-Ray on June 4, 2019.