There's kind of two ways of going about this, right? One is to think of it as "I have a functioning N64, how to I hack it into a handheld solution?". This is

There's kind of two ways of going about this, right? One is to think of it as "I have a functioning N64, how to I hack it into a handheld solution?". This is a little rough, because it'll be hard fitting the guts of a system into a handheld controller (see https://www.ifixit.com/Device/Nintendo_64 https://www.ifixit.com/Device/Nintendo_64). If you were to go this route, you're also going to have to figure out how to replace the power supply with a battery (probably some pile of lithium-polymer batteries and maybe some converters), and also some kind of display to pretend to be a TV (something like http://www.amazon.com/LCD-Display-Composite-input-Raspberry/dp/B00ETOCRSG http://www.amazon.com/LCD-Display-Composite-input-Raspberry/... ). The other is "How do I run N64 ROMs in a handheld solution?" In this case, look at an emulator (say, https://www.raspberrypi.org/forums/viewtopic.php?t=6761&p=402363 https://www.raspberrypi.org/forums/viewtopic.php?t=6761&p=40...) and then build the hardware around it. However, you have a bit more flexibility in terms of what you can pull off. You'll still have to solve the display problem though.