I can see some Bitmap Brothers influence here, love your pixels!! 

Best to avoid too much dithering and contrasting colors in such small objects...try to work more with clusters of similar brightness. Also don't think the dropshadow is doing much good here.

Of course I could not resist editing a Malone mug a bit...

Yes this was my first idea :) . But i don't know if i finally will use this faces. Seems good but i need to test with other variations and what can i do with them.

Edit: Added an improved face variation.

 Looks just like those faces in speedball 2. Cool!

I personoly think that it looks like some action faces like the one in doom.