This looks amazing! The pose and colors are both stunning, and the shading is done perfectly! You have a great style of drawing skies, and you really captured the raw power in the scene. Keep up the good work!
The greys you've used for the shading on his robes looks a wee bit dodgy but the rest of the colours work wonderfully, they give off a sense of sunset which is a perfect colour balance for this scene bringing the orange and blues from air bending and the orange and reds from fire bending and giving orange and purple plus they look quite natural