Celebi is a green fairy-like creature. It has round toeless feet, three-fingered hands, and clear wings on its back. It has a round head that comes to a curved point. It has large baby-blue eyes with thick black rings around them, and a pair of green antennae with blue tips.
Often found in forests, Celebi is a Mythical Pokémon, known in legend as the "Voice of the Forest." It is able to travel through time and exist simultaneously throughout time, and plant life flourishes wherever it has been. As seen in the anime, it is able to bring deceased Celebi back to life and restore plants to perfect health. It was shown in Pokémon Colosseum that Celebi has the power to instantly cause the Purification of any Shadow Pokémon and can be summoned at Relic Forest with the melody of a Time Flute. Despite living in forests as its guardian, Celebi only shows itself in areas and times of peace. It has been regarded that as long as Celebi are seen throughout the world, a prosperous and bright future is still in store for the Pokémon World.
The Masked Man aimed to capture Celebi and use its time-traveling powers to reunite one of his Pokémon with its deceased parents. Although the Masked Man managed to capture Celebi, the GS Ball holding it was destroyed by Gold, freeing it from the villain's control. Afterward, it would appear to help in the Ruby & Sapphire and HeartGold & SoulSilver chapters. Celebi made its debut in The Last Battle IX.
In the Pokémon Gotta Catch 'Em All manga
Shu caught a Celebi in Pokémon Gotta Catch 'Em All but released it afterwards.
When a Poké Ball is thrown, there is a 1 in 251 chance of Celebi appearing after all these requirements have been fulfilled:
Unlock all 25 characters
Unlock all 29 stages
Beat all 51 events
Unlock the score display (by reaching 5000 KOs)
It does not affect the battle, but the thrower of the Poké Ball will earn a bonus and trophy of Celebi.
"Celebi has the power to travel through time, and thus wanders from one age to the next. It is considered a deity by the forests: plants and trees are said to grow in unimaginable abundance wherever Celebi visits. Like Mew, Celebi is a Pokémon shrouded in mystery. Its special techniques blend grass and psychic powers."
When a Poké Ball is thrown, there is a 1 in 493 chance of Celebi appearing. Like the other "secret" Pokémon, it drops collectible items; in Celebi's case, it drops trophies.
"A Time Travel Pokémon. Celebi can travel throughout time and inhabit multiple places simultaneously. It is said that it appears only during times of peace, greeted by a flourishing of grass and trees. Two turns after Celebi uses its Future Sight move, the foe is bombarded with psychic energy. This proves to have a devastating impact on any Pokémon."
This Pokémon has the unique ability to travel through time to the past or future. However, the only times Celebi wants to visit are those of peace, so catching sight of Celebi in one of the beautiful forests it frequents is a good sign indeed. Perhaps it's mankind's responsibility to create the kind of time Celebi would want to visit.
Pokémon Super Mystery Dungeon: A regular Celebi appears with Ampharos and Jirachi of the Expedition Society to transport the player and partner out of harm's way before Nuzleaf and Beheeyem get a second chance to petrify the player and partner after their return from the Voidlands. Celebi explains that Dark Matter once threatened to attack the Tree of Life which would have resulted in the planet's collision with the sun, but was stopped by the efforts of a human and a Pokémon. Celebi theorizes this same human was brought back to the present by the ancient Mew. Celebi also reveals that the Harmony Scarves worn by the player and partner were made using materials from the Tree of Life; their temporary evolutions were triggered as a result of the Tree's power. Later, Celebi helps assist many other Pokémon in stopping the ascent of the Tree of Life into the sun a second time. It, along with the Shiny Celebi from Pokémon Mystery Dungeon Explorers of Time, Darkness, and Sky, are recruitable after completion of the main story via the Connection Orb.
This Pokémon was unavailable prior to Generation II.