It's trivial to play vintage Nintendo games if you're not picky about what devices you use. But what if you miss the look and feel of the original Game Boy? Wermy has an answer: build a Game Boy that does it all. His Game Boy Zero modification uses a Raspberry Pi Zero, a modified game cartridge and a whole lot of drilling to emulate classic NES, SNES and Game Boy titles (up to the Game Boy Advance) while preserving most of Nintendo's original look and feel. On the outside, the only concessions to modernity are the 3.5-inch color display and the stealthily integrated buttons needed to play some newer titles.
There aren't detailed instructions available, but the hardware hack is relatively easy due to the nature of the design: the handheld was so big because it had to accommodate 1989-era handheld technology. A Raspberry Pi Zero, an SD card slot (in the cartridge) and a lithium-ion battery are comparatively tiny. If you're willing to gut a Game Boy and have a knack for electronics, you can likely recreate this yourself. The creator is answering questions in the YouTube video's comments, too, so you can get help if you're willing to give it a shot.