The transfer pak allows you to take data from a gameboy game and put it into a N64. Currently Mario Golf and Pokemon Stadium accept it. Perfect Dark will allow you to take your picture (with the gameboy camera in the transfer pak) and allow you to take your own features and put them on the character! Although pokemon stadium has one included, you really need two to do absolutely everything (trade faster, battle easier, not have to turn on and off the N64 to switch game paks for the gameboy tower.