Bomb Frog

[Ego]

How this could possibly relate to an ecology project, I don't know. But that's beside the point.

I think the first, and biggest problem, is that it doesn't really look like anything. I can vaguely see the "frog" in the head, but the body, well, looks like a block. With yellow shoes. What even is that circle thing there, an arm? I'm sorry, but I just don't really understand what's what.

The biggest ART problem on it is that your light grays are, well, too light gray. By a lot. The top one is almost indistinguishable from white(f8f8f8 is not far from ffffff) and the second brightest blends into the white background until you zoom pretty far in. I understand the draw of white electronics, but I'd darken the grays a bit and increase the contrast.
You have a good feel for the basic mechanics of spriting(shading, AA, lightsources) but I note a couple of inconsistencies and issues. You have a lightsource contradiction on the outline of the eye, with the lighter portion being to the right, unlike the top-left lightsource. I also don't think it's a good idea to use the darker outline around the eye at all there, even to make it stand out. Your lineart in many places is simply uneven or boringly square.
I recommend making the upper jaw less round, as frogs don't have perfectly round heads, rounding out the bomb, and, well, making the body more interesting somehow. Also, the head looks huge on the body. The dithering you use up top is entirely unnecessary, and without contrast, unnoticeable as well.

I hate that blue you use on the bomb. Not how you use it, you actually hit the right contrast on that, which is hard, and ration it out alright. I just hate the color, I find it never looks good. When contrasted with the saturated red, it just gets worse. De-saturate a bit, it'll cool it out. I don't even know what that red IS. I'd assume its a fuse, but that doesn't make much sense as the robot lacks a method of igniting an external fuse.

Your outlines puzzle me. They're hard in some places, super soft in others. On bottoms you use black but never tops. I think that's crazy. As spriters, particularly starting spriters, some feel obligated to always use black at the bottom of their palettes. Just make the black another shade of your grays, and it should come much smoother. As it is, there's a huge jump between your last gray and black, and even more between black and the yellow on the tail. Its too abrupt. Also, if some are soft, all should be softer, if some are hard, make it all hard(don't mistake this for hard/soft shadows, that's alright, just make the outlines natural.)

One thing that is unclear to me; is he organic? Because he looks robotic(also organic creatures aren't born with bombs for jaws). But if he is artificial, well, he looks like he popped out of a plastic iPod factory. I, for one, would make him out of metal, and show off the metal as much as possible. Make it shiny, metallic, OBVIOUS, it'll define him as a robot. As it is, I can't tell if it's the wierdest species on earth or a deadly manmade weapon.

Also, your perspective is weird. The head seems perfectly horizontal, full profile view, while the body is at a, what is it called, 3/4 view or some such. Whatever it is, they don't match.

I've made an edit showing how I would change some stuff.

I didn't touch anything below the neck other than color, and I chose to keep the fuse for some reason(although I made it obey gravity). I hope I've helped!