This exists. No, seriously. A platform game involving diapered ponies. As if the diaper fetish wasn't fucked up enough as it was... It's called
Super Crinkle Pony Adventure and it's made in Unity.
Out of morbid curiosity, I played it for a few minutes. It's crap. And not just because of the blatant diaper fetish. It's clearly in beta and it's not at all polished. When I fell in to the water and died at one point the game glitched and I got stuck in a death animation.
Everything has a freaking diaper on it. The ponies, Gilda the Griffon, the enemies... your death animation is a pony crapping in her diaper, and there's an even dumb RPG battle where you fight Trixie as Twilight Sparkle. The level select screen has a couple of other platform based stages with Twilight Sparkle and a cutscene viewer, both a work in progress.
I'll even post a picture. I'd post more, but the attachment uploads are acting iffy.