This code is a bit complicated. When it says to 'hold' a button, keep holding it until you are told to release it. So, after turning on the game, on controller 2, press the A button. Now hold Up, then hold A, and then release Up. While still holding A, press B. Now release A. Hold Up again, press B and release Up. Press B. Hold Right, then hold B, and then release Right. While still holding B, press A and then release B. Hold Right, press A 2 times and then release Right. Hold Left, then hold A, release Left. While still holding A, press B, then hold Down, press B again, release A, hold B, release Down and, on controller 1, press Start.

If done right, "Monitor On" will appear on the title screen. Now while playing, press Start to pause and use the 2nd controller's crosspad to modify the lower-right values and select the appropriate cheat.