How to Get Pokemon Celebi on Pokemon Crystal Version
- 1). Talk to Kurt in Azalea Town to ensure he's not currently occupied with making any Poké Balls for you. Save your game and shut it off.
- 2). Plug the Game Shark into your Game Boy Color and connect the "Pokémon Crystal Version" cartridge into the Game Shark.
- 3). Power on the Game Boy Color and go to the code entry menu. Enter the code "91C089DA" without the quotation marks, and then start the game as normal.
- 4). Speak to Kurt again and he will hand over the GS Ball.
- 5). Proceed directly to Ilex Forest to the west of Azalea Town and approach the shrine near the forest's entrance to encounter Celebi. Use the GS Ball to capture it.
Source...