The 2-Player panel
The 2-player panel is for games where two people play at the same time (duh). Games like Rampage, any of the scrolling fighter games (Simpsons, TMNT, etc.), as well as the other 2-player fighters (Mortal Kombat and descendants). It also is for games that had two joysticks as their control scheme. Games like Battlezone and Robotron.
It gives each player a set of six buttons with the joystick on the left. That seems to be the pattern that most of the 2-player beat-em-ups used, so that seemed like the natural way to arrange it. My choice of button arranging doesn’t quite match the two-rows-of-three layout that a lot of the fighter games used, but I hope it is more or less easily adaptable. Honestly, I don’t play those games.