The Transfer Pak let Pokémon Stadium transfer creatures from Game Boy Pokémon games to the Nintendo 64.
The accessory connected a Game Boy cartridge to a Nintendo 64 controller. With Pokémon Red, Blue, or Yellow inserted, players could use their own trained Pokémon in Stadium’s 3D battles and manage them through the game’s compatible features.
The Transfer Pak was different from the Game Link Cable, which connected Game Boy systems to each other. It was also different from the Rumble Pak, an accessory that added vibration to supported Nintendo 64 games, and the Memory Pak, which stored save data in certain titles.
Pokémon Stadium used the 151 Pokémon from the original Game Boy games and included battle cups, a Gym Leader Castle, and mini-games. Its connection feature helped bridge handheld progress with console presentation and made the Nintendo 64 version especially memorable.