Nintendo · 1998 · Nintendo 64
A controller attachment that let Nintendo 64 games read Game Boy cartridges — most famously so players could battle their own Pokémon in 3D in Pokémon Stadium.
The Transfer Pak plugs into the expansion port on the back of a Nintendo 64 controller and accepts a Game Boy or Game Boy Color cartridge, allowing a compatible N64 game to read and exchange data with it. It was released in Japan on 1 August 1998, bundled with Pocket Monsters Stadium, and in North America on 6 March 2000 with Pokémon Stadium, followed by Europe that April. Pokémon was the reason it existed. Pokémon Stadium could load the creatures a player had raised in Pokémon Red, Blue or Yellow and show them fighting in 3D on the television. The Stadium games also include a built-in Game Boy emulator, so the Pokémon games themselves could be played on the N64 through the Transfer Pak. Other games used it to link portable and console versions: Mario Golf and Mario Tennis could transfer characters from their Game Boy Color counterparts, and Perfect Dark unlocked cheats when connected to the Game Boy Color version of the game. In all, twenty games supported the accessory — eighteen N64 games and two for the 64DD — but only six of them were released in Western markets.