The Transfer Pak connected Pokémon Stadium on Nintendo 64 with compatible Pokémon games on Game Boy. It plugged into the back of an N64 controller and accepted a Game Boy cartridge.
In Pokémon Stadium, the accessory let players use Pokémon from Pokémon Red, Green, Blue, and Yellow in three-dimensional battles. It also supported features such as viewing, organizing, and storing Pokémon connected from the handheld games. Without the accessory, much of Stadium’s appeal was limited to its built-in battle content.
Nintendo first revealed the Transfer Pak at Space World 1997. It shipped in Japan with Pocket Monsters Stadium in 1998 and later accompanied Pokémon Stadium’s English-language release in Western markets.
The Transfer Pak was not a device for playing Game Boy games directly on a television. That role is more closely associated with accessories such as the Super Game Boy. The Transfer Pak instead provided game-to-game connectivity, an important early example of linking a handheld game with a home-console title.