Number 13 is two Death Stars and a stormtrooper.

Death Star Stormtrooper mash-up by John LeMasney via lemasney.com

This one was a lot of fun. So I was looking for inspiration, as I often do, in my RSS feeds in Feedly, and lo and behold someone or other was making reference to the Death Star, and how much it looked like some cellular structure or whathaveyou. I saw a face. I did some research and found some great larger sized photos of the Death Star, took the best one and imported it into Inkscape, bitmap traced it (threshold), halved it using the node tool, duplicated it, flipped the duplicate, and I had my ‘eyes’. Then, I tried a simple “have a happy day” smiley smile, but it wasn’t working. I went out and looked up some higher res images of Darth Vader, Stormtrooper types, and the Fetts and clones. The stormtrooper worked best. I brought in the image, traced the bitmap (outline) and removed the top half of the mask using the node tool, then applied a white fill to the outline. There you have it!