Had a bit of a head ache with the controller plug.
I set up a pin adapter with paper-clips and some clip on leads ( from a logic analyser kit).
I some how managed to dislodge the 5v rail (in the controller plug) with a paper clip, I suspect that the knock off SNES controller wasn't built particularly well to begin with.

I ended up soldering on a header to the PCB of the controller for testing. I manage to place it so the PCB still fits in the case.

(Image: igorkromin.net : Converting a SNES controller to connect to a NES controller port)

The pin out is pretty much what you need for a Parallel to Serial Shift Register which is exactly what's in side the controller.

The tutorial on shift registers on the Arduino site actually works fine for the first 8 buttons in the controller.
https://www.arduino.cc/en/Tutorial/ShftIn14