Ever since I submitted a sort of MLP:FIM OC called Katana (Link), I've been letting the idea slowly change and evolve in my head, until eventually this picture was the result. It was also good practice for musculature. The larger picture was her original clothes design, but I think the smaller one to the top right was more ninja/fighter-esque.
Also she's change a bit as well: she's more thich set then most ponies and is also slightly taller; and her name is now Tonfa, after the weapons she uses.
(I drew her anthro so that if the MLP:FIM fad blows over, I can still use her in my artwork...plus I think toned women are attractive).