Tell you what. I'm going to kinda go aggainst the norm and actually follow the rules of the sprite critique thread. But first:
Your sprite is masterfully done. It is extremely detailed and the shading is absolutely superb.
However.....
As in with everything we do, nothing is perfect. Your sprite is basically done, but, if I may, I have a few points of correction.
First, I enjoy how you used a simple color scheme. Most novices (not saying you of course are a novice) would use way too many shades for the sprite. Well done.
My point is in the outline. I feel your sprite would look even better if you removed all of the black in the outline and replaced it with either a dark blue or a dark grey. The black points are not well connected with the shading, but this is a feat in itself. That is why most spriters go with the no black outline approach. It removes any spots of error or pixelation, and I think you'll find that you'll enjoy the sprite more.
Also, the mouth can't be destinguished as open or closed, so either a darker or lighter shade should be used, whichever one you prefer.
Finally, Diaruga's front, left leg has somewhat of a problem. The toe closest to the inside of its body is missing a dark shade on the bottom. I would just darken that up a little on the outline.
Note that I am being extremely picky. I am only giving you suggestions if you want to change something truly superb into something amazingly breathtaking. Otherwise, nicely done my friend.