Homemade portable N64 handhelds aren't a new invention, but when YouTuber Handheld Gameplayer decided to embark on creating his own, he was aware it would be quite a challenge.
His focus was to create a system which could be used for gameplay capture for his channel, but retain that handy portable form factor. Because the unit wouldn't be leaving the house, there was no need for an internal battery – which was a good thing, as Handheld Gameplayer didn't want to cut down the N64 motherboard (a common tactic for modders which is quite difficult to pull off successfully) as this would be his first attempt at such a build.
He then fashioned a 3D-printed case, found some buttons (the D-pad is taken from a Game Boy, for example), grabbed the required parts from an N64 pad and put it all together – with the most arduous task being the process of re-soldering the 48 wires for the cartridge slot, as it would be relocated to the back of the device.
Despite all of this effort, on the first boot, it wouldn't work. After checking all of the connections and re-wiring the cartridge slot twice, Handheld Gameplayer came to the conclusion that at some point during the install, he had damaged the N64 motherboard. After leaving the project for a few months, he eventually found another donor N64 with a damaged shell and revived the mod. Success!
What makes this mod all the more fascinating is that Handheld Gameplayer was clearly learning as he went along; sure, a lot of the pathfinding has already been done by others, but the process of getting this thing working is still interesting to see.