We write about the alternate Equinoxian universe created by Riygan on Deviantart.
http://riygan.deviantart.com/
Here's some info about the Equinoxian ponies:
They're mutated versions of the normal ponies, in a world where Celestia became corrupted and spread a type of mutagen gas. She soon became Queen Blackhole.
These ponies live in a dystopian world where everypony has some type of strange mutation.
(For example, Rarity became Stone. Stone has snakes for hair, and has the same abilities as Medusa. Stone has 3 eyes.)