Where do you get surf in Pokemon Yellow?

In Pokémon Yellow, you can obtain the Surf ability by using the Surfing Pikachu feature. To get Surf, you need to participate in the Pokémon Stadium game for the Nintendo 64 and win the Pikachu Cup. Once you have a Pikachu that knows Surf, you can transfer it back to Pokémon Yellow using the Game Boy Transfer Pak.