Pokemon Yellow Version: Special Pikachu Edition
Bypass Cycling Road Guard
To get onto the Cycling Road without needing a Bicycle, simply hold Left while the guard warns you that you must have the Bicycle to enter Cycling Road. (If you already obtained the Bicycle, this still works if the Bicycle is in the PC.) In doing so, you will bypass the guard; if you continue onto Cycling Road, you'll still ride a bike.
Contributed By: KeyBlade999.
Have Pikachu instantly like you!
When you first start your game, you will have 1 potion in your pc that's in your room. Get it out. Continue playing the game untill you get Pikachu but haven't battled Gary's Eevee yet. Use the potion on Pikachu 5 times (even though it won't have any effect). Fight Gary and WIN. After the battle, when your Pikachu comes out of the Pokeball. He will like you.
Contributed By: PyroEnthusiast.
The Old Man Glitch
This glitch requires you to have the Badges allowing the use of Fly and Surf, and Pokemon that can use these moves. You must also be able to reach Fuschia City or Cinnabar Island. First, head to Viridian City and speak with the old man near Route 2 who will teach you to catch Pokemon; view his tutorial. After doing so, Fly to Fuschia or Cinnabar and Surf to the Seafoam Islands. Once there, Surf on the coastline of the islands. As you Surf, you may encounter a number of odd Pokemon. These Pokemon will differ, depending on the name you used as that of your Trainer. For example, the name "DANIEL" can make Snorlax or Electrode appear, among others. However, a common characteristic of them is that they are often above Level 100 and thus very powerful: if you manage to catch one somehow, you essentially have a very powerful Pokemon, and can even level it up further, as high as Level 255. (Note that some Pokemon may evolve into glitch Pokemon because of this.) That is the first benefit of this simple glitch. Most people, regardless of name, should be able to encounter one of two Pokemon: Missingno. or 'M, both of which are glitch Pokemon. These two have special effects on the item in the sixth slot of your item bag, but that effect depends on whether you catch or defeat the Pokemon. If you defeat the Pokemon (or otherwise just do not catch it), the item in your Bag's sixth slot will be changed so that you have 128 of it; if you catch it, you will have 255 of it. (This is assuming you use an item that you can have multiple ones of.) This is very useful for mass-cloning valuable items, such as Master Balls, Rare Candies, or PP Maxes, or to clone TMs to sell for obscene amounts of money.
Contributed By: BOBtheDEATHfrog.
Get the Diploma
Complete your Pokedex (Mew is optional) and visit the game designer in the Celadon Mansion. He will give you a diploma as a reward.
Contributed By: infernohit.
Get through grassy areas without a single random encounter.
Once you've obtained the HM Cut you can use it to teach some of your pokemon the attack of the same name.
This ability now cannot only be used to cut down certain trees but also to get rid of any grass so you don't have to bother with any random encounters.
When saving and loading or leaving and reentering the area you used cut in, the grass will have returned.
Contributed By: KeeperBvK.
Pikachu's Beach Mini-Game
Use the Pikachu from your Pokemon Yellow in every match in the Tournament mode of Pokemon Stadium. Pikachu should learn Surf. Now go south of Fuschia City and into the house at the beach. Talk to the man inside. Make sure Pikachu is in your party. You should be able to play a mini-game.
Contributed By: All is Fair in Love and War.