What if someone did a Crossover with Gravity Falls and MLP FiM! XD oh man, i can see Mabel riding Rainbowdash. XD LOL. oh and Pinkie pie playing with Mabel the whole day, that'd be so funnny! They'd find how much they are alike.... anyway. I wonder what Dipper's reaction would be. =P
Who knows, maybe someone is making a crossover like that right now... =3

P.S. i don't think Rainbowdash will be too 'fond' of Mabel riding on her back. XD maybe not fond enough to keep Mabel on, maybe she'd buck her off. XD who knows.... o_O