Which accessory let Pokémon Stadium connect with Game Boy Pokémon games?

The Transfer Pak let Pokémon Stadium connect with Pokémon Red, Blue, and Yellow on the Game Boy.

Bundled with Pokémon Stadium, the accessory plugged into an N64 controller and accepted a compatible Game Boy cartridge. Players could use it to view, organize, store, trade, and battle with Pokémon uploaded from the handheld games.

This connection was a major feature because Pokémon Stadium presented battles in 3D on the Nintendo 64 while allowing players to use teams they had trained on Game Boy. The game also included four cups, Gym Leader Castle challenges, and minigames, but the Transfer Pak was central to its cross-console identity.

The Transfer Pak is easy to confuse with the Game Link Cable, which connected two Game Boy systems directly. It is also different from the Rumble Pak, an N64 accessory that added controller vibration. Pokémon Stadium was released in Japan in 1999 and internationally in 2000.