I have no idea how in Equestria I managed to do this… Armed with nothing but my Twilight Sparkle colour guide, a vector of Luna by lixr (only used for visual and colour reference), a vague idea of what I wanted and a screen cap of Twilight's flank this just sort of happened. Like I was possessed by somepony else!

No base sketch, just wish I had a tablet. This seems to be working for me :) Still not happy with the proportions, especially Luna's legs and hooves but I just let it evolve without going back and fixing stuff.