Amnesia Psyduck:
Get all 151 Pokemon in the hall of fame.

Hyper Mode:
Go to the kid's club. Then go to 'Who's The Best.' Select the Hard difficulty. Now instead of playing 3 games, play 5. But you can NOT let the computer win at all. You have to win all 5 games! Then you will have the Hyper Mode as a new difficulty setting!

Surfing Pikachu:
First, get to the Round 2 Prime Cup Masterball Challenge. Make a Pikachu one of the 6 pokemon on your team. This Pikachu must be from a Game Boy Pokemon game pak. It cannot be a rental pokemon. It also cannot be registered anywhere on your Pokemon Stadium game. So, do NOT register this team when you are done picking it. When you begin to fight, you must make Pikachu one of the three pokemon you select for all eight battles. You cannot use any continues. Also, you cannot save and quit anytime during the cup. If you are successful, you will be rewarded by being taken to a special screen where you can teach Pikachu surf.

Talking Pikachu:
Upload Pikachu from the yellow version of the game to Pokemon Stadium. When battling, Pikachu will say its name and have different moves. Note: You must go into battle for this to work. Do not register Pikachu.

Flying Pikachu:
At main menu press Up, Up, Up, Down, Down, Down, Left, Right, Left, Right, Start and you automatically get Flying Pikachu!

Get Pokémon for Game Boy game:
Complete one of the Gym Leader Castles of the Elite Four or your rival to get one of the following random Pokémon that can be transferred back to your Game Boy Pokémon game:
Eevee
Hitmonlee
Hitmonchan
Squirtle
Charmander
Bulbasaur
Omanyte
Kabuto

Dark Pokemon:
At the game title screen quickly press Up, Up, Right, Up, Left, then Down. You should hear a pika pika now all of your Pokemon are black or dark.

Hints

Colored Pokemon:
To change the colors of your pokemon try changing the names. For example; use lower case letters (ie: poliwhirl) change the syllables (ie: Drillbee) or just plain leave a part out (ie: pika). This can really alter the Pokemon's looks...you can even get a Pink Mewtwo!

Change Background:
After unlocking the Doduo and/or the Dodrio mode, when in Game Boy tower, play your game then press Z.

Rent Mew:
Beat the Gym Leader Castle, plus beat all the cups in Masterball and you will have unlocked a new gaming mode and a new rental pokemon. Mew is now a rental pokemon. He can only be used in prime cup, Gym Leader Castle, and Free Battle (prime cup rules only). You will also have a new title screen.

The Perfect Overall Rental Team:
Electabuzz
Persian 
Alakazam
Charizard
Cloyster
Aerodactyl

Fast Gameboy Tower:
Beat one of the two major cups and you will earn a fast Gameboy tower! Beat both and you will earn a really fast Gameboy tower press C-Right to activate them.

Attack First:
Immediately after you choose a move and you want to go instead of the computer, hold L and press A. This works about 50% of the time, mostly in the Pika Cup.

Pokemon Quiz Academy:
If you look closely, next to the Pokemon Lab there's another building. First complete the Stadium, Gym Leader Castle and get Hyper mode on Kids Club then when you choose either to Battle Now, Pokemon Stadium or VS Battle press Up, Left, Down, Right and you will hear a Pika sound. Now you can go to the building. It's a pokemon quiz academy.

Gameshark Codes:

Enable Code (Must Be On)
DE000400 0000

Infinite HP All Pokémon
81285A10 007F

Infinite HP
800AE562 03E7

Max HP
810AE586 03E7

Level 99
800AE584 0063

Infinite 1st Spell
800AE580 00FF

Infinite 2nd Spell
800AE581 00FF

Infinite 3rd Spell
800AE582 00FF

Infinite 4th Spell
800AE583 00FF

Infinite HP
800AE5B6 03E7

Max HP
810AE5DA 03E7

Level 99
800AE5D8 0063

Infinite 1st Spell
800AE5D4 00FF

Infinite 2nd Spell
800AE5D5 00FF

Infinite 3rd Spell
800AE5D6 00FF

Infinite 4th Spell
800AE5D7 00FF

Infinite HP
800AE60A 03E7

Max HP
810AE62E 03E7

Level 99
800AE62C 0063

Infinite 1st Spell
800AE628 00FF

Infinite 2nd Spell
800AE629 00FF

Infinite 3rd Spell
800AE62A 00FF

Infinite 4th Spell
800AE62B 00FF