Sorry I had to make another post, I just had to make sure that everything I posted won't lose everything by accident.
Here are two stories made by Sharkrags, the one who did the Gilda and random girl into griffons and a woman to a filly by Cheerilee.
The first one I haven't read but it's about Zecora tricking some guy into drinking a potion and turning him into a mare... I think.
http://www.fimfiction.net/story/2080...ted-baja-blast
This next story about a girl who turns into Rule 63 Discord/female Discord or Discord's daughter/niece, Eris, with a much more unique design. By unique design, I mean having much more different details from Discord besides having a feminine head and hair. Here's what Sharkrags has been using as his cover art which is a preview of what the girl who turns into Eris looks like:
http://www.fimfiction-static.net/ima...png?1411800381 See her head is more of a mix of dear and wolf instead of goat and horse like. And there's more to it than that by the time the transformation is over. Anyway the story is about a guy meeting a strange girl who has strange abilities and has an affinity with causing unexplainable mischief everywhere she goes and now that he has attracted her attention by being the only one who would talk to her (and not cluing her in about where's he's going), his trip has taken a turn for the interesting. I really like this TF as it turns out that the more power the girl uses the more of chance she has of turning into Eris. Read this thrilling story on fimfiction since it's easier to read in this site than on FA and you don't need to join to read it... maybe.
http://www.fimfiction.net/story/217549/my-name-is-eri
Though if all you care about is the transformation. Then read this chapter of where it begins half way through it where she just grow the horns in it:
http://www.fimfiction.net/story/2175...ri/surprise-me
But the real transformation has its own chapter by itself and it's really erotic and has some great details to the changes. The only parts of the chapter that's missing are the changes in the legs and when the tail starts growing as the main character just notices it when it was halfway done. If you just want to read about the transformation then it's right here in this chapter.
http://www.fimfiction.net/story/2175...illainous-body