I've long thought this would be a fun costume to build and, even though I only had 24 hours to make it happen, I was confident I could get something working even if it wasn't playable. In the end, it went surprisingly smoothly and I was able to get the buttons working minutes before the party. I even had time to cut arm holes (buttons were the priority though)!
I was confident I could build the body of the costume. It's a box with a picture on the front! So, my first step was to check that I could get a Gameboy emulator running on an old laptop and get the ROM loaded.
I installed Ubuntu on the laptop, downloaded the Gameboy Emulator, gngb, and booted up the ROM. It worked great first time (phew, was worried it'd take hours!). Gameboy emulation seems to be spot on.
Then I found a photo of the front of a Gameboy and used PosteRazor to print it on multiple sheets for gluing up. I usually like to paint and sculpt my costumes but I didn't have time for that this time; printing the front saved several hours of work.
Then it was just a matter of gluing it up and pasting it on the front of a suitable box. Couple of hours into the build and it's already a (basic) costume; now the pressure was off!