2013 is the subsection for sketchbook fillers from year 2013 and the first half of year 2014 (Dan apparently forget to create new subsection on start of 2014). There is no specific topic for this subsection.
It is 77 pages long, starting with EGS Sketchbook Comic for 2013-01-01 and ending with EGS Sketchbook Comic for 2014-07-31.