This one is a large asteroid i drew for lv3 of Xymati.  It splits apart to reveal a "core" weak point (I might include it in an animated GIF later) that proceeds to spam bullets at you.  Meanwhile, the two asteroid halves try to crush you!  Sadistic gameplay elements are a beautiful thing in shmups. 

My favorite part of how this pixel turned out is the ambient wraparound lighting at the bottom of the asteroid.  for a while I had left it the same tan hue as the rest of the asteroid.  Then I experimented with changing it to different colors and blue seemed to work the best.  The background is pretty basic, yet it turned out fairly decent.  It's essentially just a random spattering of pixels with various slightly larger stars thrown in.  I know that real asteroids are nearly never as symmetrical and evenly proportioned as this, but I figured since it splits apart that I could get away with it.  No one ever said a shmup required realism.  ;)