Also on Fanfiction.net under the username "HaterAid" The Doctor drops into Derpy's life. Literally. As he struggles to get used to a new body, Derpy struggles to help in any way possible.
Now he's on a mission to save the universe. Well, two universes. Sort of a big ball of wibbly, wobbly- you know the rest.
Listed as 'Human' but it doesn't start out that way. I would tell you why, but...
Spoilers.