Surf can legitimately be taught to any Generation I Pikachu by completing the Master Ball division of the Round 2 Prime Cup while meeting the following requirements:

• All of the Pokémon must be selected directly from a Game Pak. The Pikachu can come from any Generation I game.
• Continues may be used, but the game cannot be saved.
• Pikachu only has to be selected for the final battle and does not have to take part in the battle.