Well, since the lineart isn't yours, I'll just jump to critiquing the internal shading first.
The color choices are interesting, and overall pretty cool. What doesn't work though is that the second lightest color is pretty close to the first lightest, and pretty far away from the third lightest. It makes a weird cylindrical effect of the shape, so making that more averaged between the 1st and 3rd shades should fix that more. In addition the very darkest shades are almost identical, so that two (possibly three?) colors look like just one, which isn't good.
The dithering is inconsistent. In some places you use a perfect 50/50 pattern, in some places the dithering seems either weirdly stylized or even random, and in some places there's either really sparse patterns or no dithering at all between clusters.
The eye is what needs the most work. Considering the style of the rest of the piece, a pixel quad as the pupil and the rest being pure white won't cut it. Perhaps reference some "creepy eyes" on google images to get some inspiration, or just play around with making the pupil interesting and giving the iris veins? Just some ideas.
Can't do an edit until later today, I'm on a mobile phone
