Pretty awesome color mixing here! I think you need to have less dithering, or to say, more 'solid color to dither' ratio mainly on the jaw. I never liked dithering touching an outline and I believe flat colors would help a bit there to visually clarify. The actual ice and reflections of the pumpkin in it are ace as far as I can tell.
I would also suggest just putting black inside the eyes and in parts of the mouth, more darkness, to signify more depth.