It appears that this was either drawn on and aa'd to a black background or your monster has a stripe down its back. If the black was intended as selout, there's way too much of it on the back and head and neck.
Also, I think this needs more contrast in some areas. Specifically, your highlights should probably be a bit brighter and your third darkest skin tone, which seems to be the lightest shadow, could probably be a bit darker. Some hue variation might also help make this critter "pop".
Lineart wise, the only thing that jumps out at me is that you should probably see a bit of the top of the back foot, since the perspective on this guy implies that the ground is going up as it gets farther away. I suppose this is a basic enemy, considering it has no arms and would therefore probably not be particularly vicious.
Overall, this monster looks quite good. Keep it up!