Thanks again! I will consider this next time I draw pixel art. Now you pointed it out, I can see your point. However, it still doesn't look jarring to my eyes, so maybe it's more of a personal preference thing than anything else. 

You can read about banding here, although different people have different opinions about what it is, how problematic it is and how to solve it. The common (and very vague) definition is something like 'when pixels line up in a way that effectively reduces detail'.

You could consider changing the shadow of the mouth to avoid two identical, parallel lines. When they are identical and touching, they almost look like 2X pixels, if that makes sense. And I would look at the vertical line of shadow from the ear to the top of the neck, which stops at the same height as neighbouring pixels. To my eyes, that looks a bit jarring. I hope that helps. 

Thanks! I'm new at pixel art, so I had to look up the term "banding." After an online search, I'm now vaguely aware what it means, unsure how to spot it, and totally at a loss how to fix it, even if I could detect its presence, which I can't in my drawing, I'm sorry to write.

Nice job! I think I'd do something about that banding though. :)