Pocket Monsters Stadium 2

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

Register all 151 Pokemon in the Hall of Fame.

After beating the R2 Mewtwo, go to the Gallery. Scroll down
to ''Print'' and hold L and R. Print will become ''Bonus''.
Press A to view the game backgrounds, which can be printed
off at a Pokemon Snap station.

If you nickname your Pokemon in the Gameboy game and bring it into Stadium, it will have changed color depending on what you nicknamed it!
This has NOTHING to do with shiny Pokemon, because they were not invented when Stadium was released.
Possibilities range from an orange Pikachu to a seagreen Tentacruel.

If you beat Master Ball in PokéCup or Primecup
you will get dodou speed. This allows you to play your pokemon game in pokemon tower at X2 speed.

You must win or tie 5 rounds in a row during a ''Who's The Best?'' mini-game championship against 3 CPU's on hard difficulty to unlock hyper difficulty mode.

Put the Pikachu you started with in Yellow in your party for Round 2 Prime Cup Master Ball. You MUST USE THAT PIKACHU IN EVERY BATTLE of Round 2 Prime Cup Master Ball. After you defeat the final trainer, your Pokemon will be put in the Hall of Fame and Pikachu will learn Surf! You can now play the Surfing Pikachu Minigame in Yellow version as well.

If you beat all the cups and Gym Leader Castle, Mewtwo will appear. If you beat him, you'll get the harder R2.

First Beat Round1 and then when you Unlock R2 you can use Mew as a rental in R2 Prime Cup Battles.