Awesome piece, Discord looks thoroughly evil and intimidating especially with the fire. Celestia is her usual epic self, and the star accompanying her really enhance the scene, I lover the poses and expressions and especially her mane! Plus I just love to see a pic with these two as enemies duking it out, so I say: Go Celestia, you can take him!
The oonly thing that seems like a shame are the rough brush strokes on the inside of Discord's left leg which partly cover Celestia's tail, they seem so out of place with the rest of the very smoothly coloured piece <3
I like he fact that Discord acctully looks threataning here, as opposed to how silly he looks in the official show (nothing bad about that, but I found him a little hard to take seriously). All in all I think this is a great piece of art Great job