Well, this is my first RP request, so go easy on me!
I'd play myself, having applied to a specialised training school after my life starts going down the pan. There, begins my slow training (by either a man or woman) to become a pony, to act, eat, think as one. Towards the end, my mind starts to become animal like, as my human thoughts slowly melt away.
I try to keep my rp descriptions brief, as I enjoy a lot in rp, and like to tailor it about what my partner likes as well! So feel free to throw in any thoughts of idea you may have!