Pixel art/Customs [Criticism appreciated]

[Coal]

I've been using tSR for a couple of years now, yet I only recently made an account. I've made quite a few pieces of pixel art yet I've recently started trying out spriting.

Here's the pixels/sprites which I'd prefer get criticism:



And here are some other examples of what I can do (Even though I'm not after criticism for these pieces) :






P.S: As you can probably tell, I quite like using monochromatic colours and palettes.
I also apologize for not all of the images having transparency. :C