Battle Moveset

A Good Moveset for Celebi would have to be this:

Attacks:

Heal Bell
Toxic
Recover
Psychic

Items Attached:

Leftovers

Preferred Nature:

Timid

Strategy Using Celebi

Celebi is very much like Mew with its base stats, but doesn't learn all the TM's/HM's that Mew could. However, its picked up another type, Celebi is part grass.
well, this moveset is pretty simple to understand. Its all about Toxicing your opponent while you keep yourself healthy with the help of heal bell(which cures status problems), Recover (which recovers HP) and Leftovers which will also recover some HP.
Psychic is for the sake of an attacking move, after all, if Celebi ends up to be your last pokemon, it needs something to attack with.
This set may have problems against Steel types but you should switch out if you come up against one. Otherwise, watch out for dark and fire types too, since he has weaknesses to both of them.
Overall, Celebi has well rounded stats and is usable in quite a few movesets, but this is quite a good moveset if you want to cause your opponent some slight annoyance while dealing slow but bad damage to him.

EV Corner:

Max out the EVs in Speed for Celebi with any remaining in Defense & Special Defense

Strategy Against Celebi

Celebi's Defenses are both equal and strong so if you attack with Super Effective attacks, you should be able to take it down

Contest Moveset

A good Contest Moveset for Celebi would have to be this for the Smart Contest best with Calm, Gentle, Careful, Sassy Nature:

Attacks:

Calm Mind
Psychic
Leech Seed
Perish Song

Items Attached:

Green Scarf

Strategy Using Celebi

If you do the attacks in this following order you should have very few problems; 1st - Calm mind, 2nd - Psychic, 3rd - Calm mind, 4th - Psychic/Leech seed, 5th - Perish song

Locations in Games

Ruby/Sapphire Unknown As of Yet Colosseum Unknown As of Yet Fire Red/Leaf Green Unknown As of Yet (Obtained on Colosseum Bonus Disk in Japan Only)

Animé Appearences

Celebi has had a couple of Animé Appearences. First, it travelled forward in time with Sammy to defend itself from a Hunter, and ends up being captured by The Iron Masked Marauder and used to destroy the city. After that, a Celebi sent Richie back in time in order to make a person not destroy a Pokémon Center. Movie 4: Celebi - Voice Of The Forest! Special 14: Another Legend Of Celebi!