bengo - your lizard looks pretty dang cool too, looks like something from Metroid now with the colors and the eye
as for the critique - form first - got it.  I can clearly see the form of the muscles of the arm. When you say adding detail in the transition from shadow to light.. you mean the half tones? for example, I see in the arm that the most dithering is at the light and mid light, while shadows and high light looks more clustered.
Yea, I am doing a set of creatures from Oblivion right now, but once I finish, I am seriously gonna try to study more regular art, including anatomy. It creates problems for me every time I try to create bigger sprites.

At the terminator line you want to add detail, where the light transitions into shadow. You'll see a lot of artists do this. Still you need to make sure, like I keep saying , the primary and secondary form is still readable through the detail.

As for anatomy studies this itself could be one! I gave you an anatomy drawover showing all the different muscles. What will help is to reference an anatomy sheet and look up 'origin' and 'insertion' for specific muscles (for instance- 'origin and insertion bicep' and you'll see it connects from the scapula to the radius, part of the lower arm, bone). You can also do something called an 'ecorche' where you draw muscle on top of a figure, typically with obvious anatomy sticking out like someone muscular or very skinny, and of course you can use an anatomy book as reference. Andrew Loomis' Figure Drawing For All It's Worth can be found online for free and has the anatomy correct for you to reference.

While it's good to experiment I don't think it has to necessarily be "random". What I mean is, you can narrow down what you want to do by figuring out what the goal of the piece is or the goal of that part of the piece. I prefer the second one since it helps point to the focal better.

I feel a bigger issue is the size of the spearmen themselves. I initially thought they were statues and not people and, to be quite honest, they still look like statues. Proportionally they're huge and on top of that they have very static poses. I say keep them as statues and throw more of them around the scene but that's up to you.

Also, you typically want bigger pixel clusters/shapes in areas that are closer to the viewer. I think the clouds have a lot of small shapes that are quite distracting same with the mountains a bit.

Sent a follow-up email specifically with the kind of work you're looking for. Link to it will be put here as well- https://pixeljoint.com/pixelart/138160.htm

Sent an email. I will await your reply.

Good edit that retains the style but I would like to clarify why I did what I did in my edit.

The reason I went so extreme with my edit was to showcase the advice I stated below (e.g. breaking the line/not using outline fully though admittedly I could've used more of an outline, using less colors, importance hierarchy and simplifying). Not sure if I fully agree on the readability, of course when you have a black outline it's gonna immediately stick out against mostly anything but, I think the lack of outline while technically "sacrificing" some readability has its own perks (related to a sense of 3dness and the breaking the line principle I stated). An outline around something will definitely make it more readable but I think ultimately it comes down to design.

Changing the bird was just to show how much you could simplify it. Keeping it the same kind of bird is fine too. The colors I chose were to demonstrate how little is really needed. I still don't think the shadow color on the jacket is needed... it's so close in value to the dark "black" outline color which is why I got rid of it in mine. This kinda decision is really up to if you care about palette size (I personally am not a big fan of limited palettes but I do think trying to limit your colors to "only the necessary" can be good practice).

So, when you're talking about volume, you've got light hitting areas where it wouldn't be receiving light (like the legs) assuming the light is coming from above (the hair and the specular on the hair indicates from above). I opted to simplify and stylize to avoid this lighting issue (that shirt in reality wouldn't be that white because it wouldn't get hit by light for the most part) though the other way would be to of course keep it consistent... but since we're at suc ha small size that could be a problem. Personally I think the change from top on the hair, to the the side on the chest and arms, to the other side light on the legs is too major of a difference. I suppose you're still technically showing the volume this way but lighting-wise will be logically confusing.

Ultimately it comes down to when there's errors or when there's design choices. Sometimes it can be a design choice and even an error could be a design choice if it arguably looks better. I felt the design choices I made helped improve the sprite over-all (I don't think the un-logic of the lighting works) or at least helped demonstrate the critiques I gave. It's up to you to decide what you want to do or how you want to tackle this. The critiques I would say you certainly want to do though is make the legs skinner make them less bent, modify the shoulders so they're not awkwardly tilted and make sure the lighting follows one direction. The lighting thing can be quite difficult though, since even in my edit the bird's lighting is slightly different from the girl's but I felt it wasn't drastic enough to be super noticeable and helps the readability of the bird (though who knows, you could probably do top lighting and it'd look fine, it's really close to that as is).