Hey guys, I've been working on a game for quite a while now and was hoping to get some advice on how to push my pixel art from being merely competent to being decent.

It's a creature brawler, kind of like Pokemon but with much more involved battles. So I have a lot of creature designs that need to be very notable and iconic.
(I also have concept art for all of these but for the sake of not flooding the thread more than I already will be, I'll only provide that on a request basis)

Creatures (I have a ton more of these, but this is a good sample of what I'm producing):
 

A Boss:


Battlefield:


In game screenshot of it all coming together:


Feel free to throw any kind of critique at me, I'm here looking to improve and I'm only going to do that with change. Also let me know if I broke any rules, I've lurked here for a while tried to follow them all but I may have done something wrong, and I'll fix that up if I did.