Extremely well set and the expressions are perfect. The background coloration adds depth without distracting. Twilight's pose is awesome except for a slight anal wanting on my part. Discord's arm clearly shows where her arm is but I still want to see it! I know that means changing the angle of the pose, so it's not neccesary. Like I said it is just an anal thing with me. I love twilight's dress and can only imagine her response when Discord put it on her. Discord's posture and expression are wonderfully set in a very smug, self satisfied way. Overall this shows your great attention to detail and fantastic art ability. The characters are done very well and the scene is hilarious.
This is pretty good, but my only problem with this is that for whatever reason the position that Twilight's face is in makes her look kindof like a pig.... not sure if that was intentional though. It might be because her eyes don't have anything drawn to separate them. The eyes on Twilight (and ponies in general) would more show-oriented be on the sides of her face kindof. When shown from the side, ponies have a bit of a bridge between their eyes and it connects their nose to their fore-head.