Pixel Mushroom from Mario Bros games.

Buildt in Sketchup; 16x16x1cm in model, I scaled it to 50% and it printed fine.

See also:

Pixel Star from Mario Bros games.
http://www.thingiverse.com/thing:582011

Pixel ghost Boo from Mario Bros games.
http://www.thingiverse.com/thing:1211037

Pixel Moon from Mario Bros games.
http://www.thingiverse.com/thing:1177844

Christmas Skull
http://www.thingiverse.com/thing:739017