I would have edited some more stuff but im kind of short on time (I lost track of time while editing this, haha), hopefully you see sort of what im trying to get across. My edit is 6 colors (four on the character and two on the gun), your original sprite had some repitition of colors and a lot of very similar hues, and did not seem like he was "guarding" the base. I used your colors and some slight modifications and changed his pose.
I brought the gun arm back because it seemed like a large gun, and made his other arm a support for it, and I bent his knees a little to make him seem more alert. I wasn't sure if the head was supposed to be a helmet or a head wrapping of some sort, so I gave him a wrap. I liked your eyes but the way I changed the head they came out looking kind of weird, im sure you can figure out how you want to do it. Your legs are also a bit conical, seeming really thin at the top and expanding down, and your waistline seemed kind of low. This might have been the reason you had difficulty with movement animations.
I feel like you might want to keep an outline around it though because I tried setting it against a darker background and it comes out looking hard to read. Upping the contrast might help with that, im not too sure. I think mine is also off balance and leaning backwards a bit but hopefully the ideas get across.
I feel like most of these crits go for your protagonist as well, I feel like he could do with a more energetic pose.
Hope this helps!