Instructions
Insert the "Pokemon Gold" or "Pokemon Silver" game cart into the Game Boy or Game Boy Color system. Turn the system on by switching the power switch upwards.
Begin the game by pressing the "Start" button. Select your "Pokemon Gold" or "Pokemon Silver" save file and press the "A" button to begin playing.
Place a Pokemon you do not mind replacing at the first slot of your party by going to the "Pokemon" menu and using the "Switch" function to move your Pokemon around. Getting Celebi requires that you replace one of your Pokemon.
Select "Save" from the options menu to save your game and turn the system off. Remove the game cart from the system.
Insert the "Pokemon Gold" or "Pokemon Silver" game cart into the GameShark device by pushing the game into the cartridge slot of the GameShark. Insert your GameShark into the Game Boy or Game Boy Color by pushing it into the cartridge slot of the system. Turn the system on by switching the power switch upwards.
Enter the code "01FBEDDO" at the GameShark code screen. The code starts with a zero and ends with the letter "O."
Begin the game by pressing the "Start" button.
Select your "Pokemon Gold" or "Pokemon Silver" save file and press the "A" button to begin playing. Celebi replaces whatever Pokemon you had at the first position of your party.