This is a video of [Joey Mariano] from animal style demoing his Game Boy pedal board. He added a D15 port to the back of the Game Boy, which is wired to each of the 8 buttons. The port is connected to a breakout box for 8 piano sustain pedals. The box also provides power to the Game Boy. The Game Boy is running the Nanoloop step sequencer. If you’re wondering about the guitar sound, he’s probably using an 8-Bit Fuzz pedal.