Surfing Pikachu
Surfing Pikachu is in Pokémon Stadium for the Nintendo 64. To teach your Pikachu Surf, reach the Round 2 mode, then enter the R-2 Prime Cup's Master Ball division.

Assemble a team that contains a Pikachu from Pokemon Yellow. Make sure not to register your team.

Beat the Prime Cup's Master Ball division using a three-Pokémon team that always contains Pikachu. Pikachu must be in all the battles, and you can't lose a single round.

You will be rewarded with Surfing Pikachu, and can access the Surfing mini-game on Route 19.

In-game reset
Hold Select + Start + B + A during game play to restart.