I'm far from being good but I can point a few flaws in the piece :
-Never ever use blakck outlines inside the sprite
-Use more contrast on the horn palette and less on the brown one
-Since there is too much contrast on the brown palette, the dithering looks obvious and useless
-Your AA is not correct, here is a quick example of how it should be done (left : yours ; right : correct AA. Still you should not use pure black)
(zoom in to see the difference)
-There's an overall lack of texture : is it made of rock ? fur ? plastic ?
