It even has a custom cartridge
This “Game Boy Zero” from YouTube user Wermy ranks way up there as far as cool custom systems go.
Besides the nice new screen and two extra face buttons (taken from an NES controller to provide a more authentic feel), the system also has external ports for USB, micro-USB, mini HDMI, and tiny L and R buttons. On the inside? A lithium ion battery and a Rapsberry Pi Zero, of course.
The way the handheld accesses games is super neat. Using a custom Game Boy cartridge that functions as an SD card adapter, it’s able to run emulated software including NES, Super Nintendo, and Game Boy Advance titles. He even went to the effort of making a professional-looking label for the cartridge.
There’s a part breakdown in the video description, and Wermy has also shared a photo album.