How do you catch Celebi?

Answer 1

Catchin Celebi in any Pokemon Game as a wild encounter is impossible. But here are ways you can obtain Celebi in various different Pokemon games.

Pokemon Crystal

In Pokémon Crystal, you needed the GS Ball which only be gotten through a Nintendo event. This would allow you to encounter an in-game Celebi in order to battle it and attempt to catch it.

Pokemon Diamond, Pearl, Platinum, Heartgold & Soulsilver

You can only get Celebi through a Nintendo event. There are also other ways, such as the Action Replay or by trading with another player who has gotten a Celebi.

HOWEVER

Starting February 21st, 2011, Celebi is available for DS download as a mystery gift in Pokemon Black and White tours and in any GameStop store. Just simply go into a Gamestop store, and choose Mystery Gift in the game menu. While here, choose "Wireless Download."

NOTE: Make sure you do not have more than 2 wonder cards. If you do, you must delete one in order to receive the Celebi.

After the download is complete, play your game and go to the nearest pokemart. Talk to the mail man in green while inside and he will give you your Celebi.

NOTE: Make sure to have atleast one open slot in your Pokemon party in order to obtain the Pokemon.

Actually I got my celebi from an event but if you look it up on bulbapedia there's a celebi egg glitch.