You do that.
I will take a TMNT/MLP crossover ONLY if the TMNT end up in the Pony's world (not the Equestria Girls route) for reaction sake.
That way they can be like, "
I know we're kinda weird, but tiny talking horses... What." Wouldn't mind seeing how odd that is to them, since they're a lot closer to human on the anthro scale and come from a world full of humans. lol