The biggest change from the sketch was curving the top of the castle wall. I think it gave it a little more of a disorienting kind of edge.
Another small change was with the dragon's tail. His name is Draco, first of all. And he isn't as tough as he tries to make himself out to be. (I've sketched out the image that will be going on the back of the postcard which will explain what I mean. You'll have to check back in a few days to see that one when it's finished.) As for the tail; I changed it. No biggie.