Quote originally posted by The Shiny Ho-Oh:
How to get all 3 starters [Crystal]:
This is one of my personal favorite glitches. It's incredibly simple to do, and doesn't take much time at all.
Start a new game, and get to where you choose your Pokemon. Save in front of the Pokeballs before you choose.
Choose whichever Pokemon you want, and head out to Mr. Pokemon's house.
Defeat your rival, and head back to the Professor's house.
Receive the Pokeballs.
Give one to your starter.
Catch any Pokemon in the wild.
Go to the Pokemon center, and deposit your starter.
Go to "Change Box" and turn off the game when the period in "Saving game, don't turn off the power." appears.
Turn the game back on, if you did it right, you should appear in front of the starter Pokeballs again. Choose your second starter.
Run directly to the Pokemon Center. Check your PC. Your first starter should be there, holding a Pokeball.
Take the Pokeball and catch a random Pokemon in the wild.
Deposit your two Pokemon again.
Change box, turn off the power at the period again.
Turn the game back on. Take your third starter.
Head back to the PC. If all has gone correctly, you should have all three starters!
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Just wanted to note that this also works in Gold and Silver.