I was perusing twitter one day when I noticed HolgaMods has a feed and was showing off different designs for Holga masks. Many were fun designs, but one really caught my eye. A diagonal mask. One shoots a roll then rewinds the film in something like a film changing bag or a dark room and rotates the mask 180 degrees and shoots the film again. For the first roll I placed the mask in a Holga GFN with Lomography CN400 film. I really like the mask and it was not terribly hard to line up the 1st and 2nd exposures. My only regret was using the Lomography film. The paper is extremely thick and I can only resume that this contributed to the pressure plate scratching the film. I recommend looking for HolgaMods online if you want a mask of your own. I think he has 8-10 designs to choose from and a better shipping rate on multiple masks.
You may guess that my first theme was the city vs lakeside