I had a few minutes before I had to leave, so I threw this together. Now I'm on the subway, so I'll type this out:
I like how much effort you're putting into the graphics. If I were in your shoes, I would approach Clash Man, something like this:http://i62.tinypic.com/16av3ti.jpg
Granted, I'm not sure about the palette restrictions here (I haven't looked at the ROM to see which parts are sprites), but...
I would change the 2B you have to 3B (this makes the teal shadow more dominant, which I think helps Flashman, looks fine on Bubble Man, and especially helps Clash Man's visor) I then cleaned up the visor, trying to give cracks that followed the curve of the glass and were affected by the highlights.
I also reapproached his helmet, so that the red would be like peeling paint hanging on the metal surface, which I think would read more clearly than red internal mechanics.
For the face, I made the jaw small enough that it would conceivably fit under the skin, had the torn skin hang over it, and instead of trying to draw every tooth, simply implied a few that were visible.
Just a quick throw together to illustrate. I look forward to seeing your sprite work.