Okay, so a couple years back somebody threw together an excellent spoof of Pathfinder called Ponyfinder. The couple of pages done in the style of the Pathfinder core book took the pony types from the My Little Pony:Friendship is Magic show and offered them as playable races for the the Ponyfinder game. Just brilliant. (I showed it to my daughter, a non-roleplayer, and she immediately said "I want to play that!!") Well, it didn't stop there. People grabbed the idea and ran with it. Various authors have created My Little Pony based material for Pathfinder. One of those is Ponies for Pathfinder by David Silver.
Ponies for Pathfinder takes the approach of making the various pony types into PC races for Pathfinder, either for inclusion alongside the existing races or an all-pony world. Naturally, this assumes that the GM and players are cool with certain conceits of the genre, but you probably wouldn't buy the book if you weren't already into it. The rules provide all the necessary crunchy rule bits for the regular pegasi, unicorns, and earth ponies and also for the uncommon breeds of sea horse, gem pony, chaos hunter, and doppleganger. There are pony feats, how ponies do as each of the classes, favored class options, racial archetypes, a pony bloodline for sorcerers, special pony magic items, equipment, pony spells, and even the gods of the ponies. The rules also cover the possibilities of using ponies as animal companions or familiars. It's really quite complete. I could totally see running this; I think it would be great at a convention or games day at a local gaming store.
All in all I was quite pleased with the care and attention taken with adapting the ponies for Pathfinder and the completeness of it all. The only disappointing note for me was that the only art is on the cover. If you're at all interested in a My Little Pony/Pathfinder mash-up then you will enjoy this product. There's something in here for everypony.