I think you can tell what the "baby" form here is and what the final form is just by looking at these, which is pretty impressive especially considering these sprites are all roughly the same size. Just in terms of pixel technique, I'd advise you to move away from single-line ranges of light and shadow - they make these designs look flat (especially on areas like, say, Blazrex's leg).

This is nice, and fast! But if you want to, you've got 6 more days to make it even better!

Some starting points: I'm sure you could get that curve on the middle one smoother. But the thing that stands out most to me is the banding/fat pixels, if you learn to fix this your pixel art will improve a lot!

Good luck :)