Angel and Demon

Ok let's get to it!

As much as I love the use of the textures on the clouds and the colours, I think there could've been more detail added, like this the clouds look flat, more like some kind of rocks I guess? Next time try to make the light appear on more places than just the edges off the clouds, that'd make them look more puffy. Also a tiny tip for the textures, as a SAI user I can recommend using the texture on the blur brush instead of the paint/air brush itself, it'll look much softer.
Now for the dragons, they seem like they're really in a great fight. Their expressions say absorbing they should, they have a lot of emotion in them. The poses look perfect, you have great anatomy and sense of composition, the placement of both characters is really nice and the shading is very well done, the color of the shadow is fitting the whole picture well. But maybe there should be a shadow on Daris left wing, because of the other one which is closer to the source of the light.
Rex seems ok to me, his giant wings bend nicely and the light going through them even shows his body silhouette, that's a very nice detail.

Overall, the picture is looking very good, seems like you put a lot of effort into it and it paid off! Everything seems to work well, the colours complement each other but not extremely which would hurt the eyes. The placement and perspective look tought out and that makes the picture even better.
Great work.