Instructions
Attend an official Pokemon event to acquire Celebi for "Emerald." Upcoming events can be found on the official Pokemon web site's "News and Events" web page or the Serebii web site's event database. On the "Serebii" event database, select "û" from the drop-down menu to see current events giving away Celebi.
Bring your copy of "Emerald" with you to a Pokemon event in order to receive Celebi. Alternatively, trade for a Celebi with other players. "Emerald" can trade with "Ruby," "Sapphire," "FireRed," "LeafGreen," "Colosseum," "XD: Gale of Darkness" and another copy of "Emerald." You will need a GameCube link cable or Game Boy Advance link cable to connect the systems for trading.
Acquire the "Pokemon Colosseum" bonus disc, which was packaged with "Pokemon Colosseum" in Japan for those who pre-ordered the game. It may be sold by retailers or secondhand vendors. This disc will download Celebi onto your copy of "Emerald" or any other Game Boy Advance "Pokemon" game you own.