The group's page used to go into more description - my apologies for not double-checking that it still had it.

The basic premise of this shared universe is that Discord, one of the cartoon's villains, took a human from Earth and dropped him in a non-human, non-pony body in Equestria. He then proposed a game to various multiversal deities that they do the same - and whichever piece was the last one standing, their sponsor would win the game and gain some measure of power, and the piece would be given a wish.

Some pieces know some, all, or none of this; some of the godly players have various goals other than simply winning the game; and I'm pretty sure Canterlot is going to get blown up at some point in the future.