Note: The following comments exclude Diababa, that is going to need to be re-done.
Well, if you are trying to do pixel-art, not too bad, you need alot of shading, some anti-aliasing, fix the creepy smile on Ordona, make the Twilit-Monster's arms, less blocky, they need to smooth out. The overall anatomy is good though. On the other hand, if you were trying for sprites, actually used in game, then those need a ton of work. They need to be compact, less detailed, and easier to make animations for.