Bat ponies are the most unique breed of pony to Equestria. Their story is one of hate, isolation, and other's fear of them being different. They are creatures of unknown origin. They are monsters in their own rights...

They are a creation of one's inner desires gone wrong.

(Something I thought about based around the bat ponies, which are these. Tagged dark for what I think is the pony form of racism, death, and other things.)