Humans.

Truth or myth? Ancient lost civilization or just an old pony's tale?

No pony has ever seen one, and most haven't even heard of them. But Lyra knows that these wonderful creatures are more than just old legends, and she's going to find out... and possibly drive her roommate insane in the process.

Stranded on a hostile, alien world, Twilight Sparkle and Rainbow Dash must depend on one another and a fellow alien castaway if they want to return home to Equestria.(originally published on FFN)