Things You'll Need
Instructions
Connect both Game Boys by using the Game Boy Advance Game Link Cable.
Travel to a Pokémon Center on both Game Boys; you can find a Pokémon Center in any town.
Walk upstairs and speak to the woman behind the desk, all the way to the right. Do this on both Game Boys.
Select "Trade Center" on both Game Boys.
Select "Yes" to save your game.
Select "Sandshrew" from the copy of "Pokémon LeafGreen." Select any Pokémon from your copy of "Pokémon FireRed."
Select "Trade." You will now have a Sandshrew on your copy of "Pokémon FireRed."