This is a remix of the Customizable Gameboy Cartridge Holder by grepsy.
This version will allow you to add a layer for your DS and 3DS games as well. This model has 20 slots. Feel free to remix with a different slot configuration.
I definitely recommend printing with ironing so that the top stays smooth and so do the slots. You may want to print with a raft because I found the corners warp I little.