Pokemon Stadium

Beat R1 Mode, and reload the game. In place of the title screen is a new one.

If you win the tournament on hard, you can get all the pokemon (including all pokegods).

Pokémon Stadium Cup requirements:
Pika Cup
Pokémon can only be between level 15-20.

Petit Cup
Level ranges between 25-30. There is a height requirement though. Height 6'8" limit and weight 44 pounds.

Poké Cup
Only can use 3 Pokémon, levels 50-55. The sum of the Pokémon's levels cannot exceed 155.

Prime Cup
Everything is legal. You can have any level, height, weight, or number of Pokémon. However, your opponents' levels are always 100.

Did you ever notice how some of the Pokémon that appear in Pokémon Stadium have different colors? The secret to the color variations lie in the names you give your Pokémon as well as your trainer ID number (assiged to you in Pokemon Blue, Red or Yellow, whenever you start a new game). While there are a few secret names that change only certain Pokemon's colors, there are a few naming tricks that result in different color variations. For example:
Use only lower caps (ie: poliwhirl)
Reverse the syllables (ie: DRILLBEE)
Abridge the names (ie: Pika)

Register all 151 Pokemon in the Hall of Fame.

Immediately after you choose a move and you want to go first instead of the CPU, hold L and press A. Note: This trick only works about 50% of the time, mostly in the Pika Cup.