Twilight Sparkle, at least 20% furry.
I couldn't grasp the proper pose, so 3D Custom Girl XP poser used for reference renders (the poser does not support correct shadows, by the way, so had to make all from scratch >_< ).
Took about 24 hours to make.
Drawn in SAI at 2013/08/27 - 2013/08/28.
Edit: Uploaded fixed and improved version at 2013/08/30.