Haha reminds me of the Diablo intro.
The legs of the raven look like they are on the same plane. Are you sure you need two pixel outlines on the raven?
On the left horn of the skull, there is a curve of light pixels at the lower left side that I don't understand. Neither do I understand the black directly above it. I guess that is because the raven is lightened from top left, while the skull is lighted from the left. And even then there's some light missing to the left of the horn.
I'm only going to mention the many dents in the horn because you're probably work on these anyway.
One more thing I do not understand: Do the horns point towards the viewer or towards the background? The legs of the raven seem to make no sense.
The skull looks great but the right eye (the bright one) deserves some attention. There are two occurrences of parallel jagged lines: white/black at the otside and lighy grey/white at the inside, to left part of the eye each. I believe you should work on these regions. And then I'm not sure whether I agree to the shading of the inner of that eye... To me it looks like there's a pillow-shaded sphere in there popping out of the eyeshell (?).
Other than that, great jaw, great raven, great nosething, great horns.
PS: I believe the snake is too much. Can't be such a cruel world if it's so full of animals that two different kinds gather at one random skull.
EDIT: The longer I look at it, the more it seems that the main problem are the legs of the raven. Make the raven sit on the horn correctly and it will already improve by a huge shot. Then shade the legs correctly and we'll see how that works out. (plus the other things I mentioned beside the shading).