N64 Trasfer pak

The Transfer Pak is a removable accessory for the Nintendo 64 controller that fits into its expansion port. When connected, it allows for the transfer of data between supported Nintendo 64 (N64) games and Game Boy or Game Boy Color (GBC) games inserted into its cartridge slot. By using the Transfer Pak, players can unlock additional content in compatible games; the Pokémon Stadium games, with which the Transfer Pak was initially bundled for sale, also feature the ability to emulate specific Game Boy Pokémon titles for play on the N64.

The Transfer Pak was supported by roughly 20 N64 games worldwide, only six of which supported it outside of Japan. Several games which initially planned to utilize the accessory were either cancelled or had the functionality removed. As a result, while recognized as one of the first examples of connectivity between Nintendo's home consoles and handhelds, the Transfer Pak has come to be retrospectively regarded as largely unnecessary by members of the gaming press.