Oh loving that expression! Perfect for Charizard, Mega or not! I really like how you've done the fire on its tail and the shading on the wings. And very nice consistent line-art on the tail, that can be really hard to do on curves!
This is very good. I, too, like the expression Mega Charizard Y has. I also like how the middle spike on the top of its head isn't too much longer then the other two, which is something that bothers me about this Pokemon normally, but you make it look so much better here! Good job