Pretty creepy design! I'd definitely suggest some lumpy shapeness on the right side where his eye is, if it was human. But I realise it's not. I'm not entirely sure what shape the skull is. But I think, inferring from the left side, there'd be a visible 'eyebrow' bump? Maybe?

What sort of texture are you aiming for? Right now he looks shiny and slimy to me. Cause of the wibbly shading and the specular.

White looks good for hair highlight with the colours you already have.

The perspective is inconsistent. Some of the buildings are isometric. Isometric means distant objects don't appear smaller than close ones. Also, the camera in iso would never see the sky, it would be pointed at the ground (assuming a flat ground).

If you'll keep the moon, I suggest you shade it to make it solid and rounded. Right now it looks like a disc.

You used an unnecessarily large pallet. I reduced the colours down to 20, and I think you could halve that (counting visible colours by eye). I recommend the purples rather than greys (so I did that replacement).

Did some re-shading and dithering, to make it look smoother (with some rough blobs).



Also I removed the alpha transparency to make it easier to work with. Up to you if you want to keep it to make it blend into a website background... but I don't think that's often great for pixel art.

I like the simple style, and I like StaticSails's edit too. I agree with Dusty that the highlights are bad (or at least too much).

Mixing pixel art with NPA is totally cool. But pure pixel art should probably be posted here.

The character sprite is very Superbrothers, but not as smoothly animated as his (their?) work. The arm jitters. It's a bit hard to read too. Is that whole grey rectangle the body? Is he holding a stick in his other (behind the body) hand? If so, consider having two different sets of frames for left and right facing. Probably feasible given the small (smaller than standard) sprite size. Would make it clearer.