Which accessory lets Pokémon Stadium transfer Pokémon from Game Boy games?

The Transfer Pak lets Pokémon Stadium transfer Pokémon from compatible Game Boy games.

The accessory fits into the back of a Nintendo 64 controller and accepts a Game Boy cartridge. In Pokémon Stadium, it supports Pokémon Red, Blue, and Yellow, allowing players to use trained Pokémon from those games in 3D battles and other features.

The connection also enabled players to view, organize, and store Pokémon, rather than limiting Stadium to its built-in rental Pokémon. This made the Nintendo 64 game a companion to the original Game Boy titles and gave players a reason to build teams across both systems.

The Transfer Pak is different from the Game Link Cable. A link cable connects compatible Game Boy systems to one another, while the Transfer Pak connects a Game Boy cartridge to the Nintendo 64 controller. Pokémon Stadium 2 later extended compatibility to Pokémon Gold, Silver, and Crystal.