Based very heavily on @jasburns' NintendoSpy, these are Arduino sketches to intercept controller data from one SNES console and send it to another.

This guide should help with more information on wiring. Once you're all set you should connect the wires to the Arduino like this:

• LATCH to pin 3
• DATA IN to pin 4 (this is from the current SNES controller)
• CLOCK to pin 6
• DATA OUT to pin 8 (this is for the other SNES controller)

• Arduino Port Manipulation
• How to control Arduino pins from registers without digitalWrite and digitalRead
• Programming for SPI
• Arduino Wireless Communication