Pokemon Yellow introduced players to a unique, one-off minigame called Pikachu's Beach. With a Surfing Pikachu in their party, the surfer in the house on Route 19 will let you play a minigame similar to the NES title Excitebike. The easiest way to get a Surfing Pikachu is through Pokemon Stadium, though other methods exist as well. Your high scores are posted in the wall of the man's house can be printed out with Gameboy Printer!
The controls of Pikachu's Beach are very simple. Use the left and right buttons to flip when Pikachu is going off of a wave. The key here is proper timing - if you try too many flips on too short of a wave (the highest amount of flips doable is three on the biggest ones), you'll crash and lose points.
How to get points
The purpose of Pikachu's Beach is to get to the end of the level with the most points you can. Do flips to get points (one flip is 50, two flips is 180, and three flips is 500) The more flips you do, the faster the screen scrolls, making it harder to predict oncoming waves. If you bail on a flip, however, you don't get the points and the scrolling slows down. A faster screen scroll is better because it leaves you with more HP at the end of the game, which gets added to your score. The HP bar starts at 6000 and constantly goes down (it's more like a timer).
Even outside of the mini-game, you have the ability to surf on Pikachu where it has its own special sprite showing Pikachu surfing on a surfboard.