After a freak storm hits Ponyville, Twilight and Spike find themselves in a world even more brightly colored than their own... the land of Oz (as in the Wonderful one, not the Prisony one). Proving themselves capable of murder, they are enlisted by the 'heroic' and 'good' citizens of this land to go on a quest to find their way home... and kill again (once more, this is the Wonderful one, not the Prisony one).
Aiding them will be a group of ponies that look oddly familiar... including an crow-buckin' scarecrow, a tin pegasus (who is 20% color than other tin ponies) and the Cowardly Flutterlion.
The only thing standing in their way? An evil witch, flying Diamond Dogs, an insane Doctor, themselves, and possibly ninjas.
Oh, and Scootaloo might get a new origin, since you all eat those tales up.