Things You'll Need
Instructions
Insert "Pokemon LeafGreen" into one Game Boy Advance console and either "Pokemon HeartGold" or "Pokemon SoulSilver" into the other Game Boy Advance and then boot up each system.
Place the two Game Boy Advance systems parallel to one another to activate the infrared link.
Use a technique like Dig or Fly to travel outside the nearest Pokemon Center in both "Pokemon" games you are running. Enter the Pokemon Center through the door on the far left.
Speak with the man standing behind the desk on the right, who asks if you want to battle or trade Pokemon.
Select "Trade." You are transported into the Trading Room. From here, select the Pokemon you want to dispose of in "Pokemon LeafGreen" and then select Celebi in the other Pokemon game. Press "A" to confirm the trade.