Hello,
for some time now i am sitting on a project which includes an old transparent Gameboy Classic. But because i only have little experience with modding, i thought why not suggest it to you.
The idea is that you have a Gameboy with a game inside, f.e. Pokémon Red, which is played by an Arduino compatible microcontroller, like the Digispark.
I already build it with a Gameboy Color, but i improvised alot.
Also i already made a thread about this project but unfortunately i didn't recieve the help i needed to finish it.
Pokémon Tamagotchi using Digispark - Help needed
In my first attempt i used a Gameboy Color where i wired the buttons to the Digispark. But because the Gameboy doesn't fit into the Gameboy Classic Box i found, i would redo all of it with a Classic.
Simmilar to "Twitch plays Pokémon" , the Arduino should press the following buttons randomly: Up, Down, Left, Right, A, B and Start.
It should be left on 24/7, on my Gameboy Color the Arduino got a Bulbasaur on level 43, but he still didn't make it out of the first village. 
I would be really thankful if you could pick this project up, so i can finish my own.
Sincerely,
Theo