Dark skies

The first thing that comes to mind is "epic" and I was going to comment that before I saw you wanted a critique.

I love the lighting in the pic, it matches the storm atmostphere quite well. And the tail, even with the odd angle the tail is done very well.

I'm a bit confused as to what the antler looking things are sticking out from his sides, going back to the sprite here [link] I realized those must be the limbs on its back. Those should be thicker, however as I said I like the spin on the tail.
Only other small detail I think needs improvement is the red triangle on its chest. It looks off center, as in you didn't curve it to coincide with the neck and chest turn.

Overall, a few proportion and angle imperfections but I love the coloring (especially with the shading and subtle highlights) and I like the simplistic yet complicated setting you've put this legendary in ^^