In order to access the special event with a Celebi in Pokémon HeartGold, it must be a Celebi that has the "Fateful Encounter" flag in its summary. If it does not have "Fateful Encounter" in its summary then it will not activate the special time travel event in "HeartGold."
To get Zoroark you must have an fateful encounter with one of the Shiny Beasts (Entei, Rakiou etc.) The fateful encounter itself is an event.
The Pikachu-coloured Pichu, with a fateful-encounter flag (the one that can activate the Spiky-Eared Pichu event) can only be obtained via event.
You need a 'Fateful Encounter' Celebi.
Yes, as long as the Arceus in question has the "Fateful Encounter" flag in its summary then it'll be able to access the Sinnoh Trio event.
You need a fateful encounter one
Get a Zorua. to do this, you must have a fateful Encounter Celebi in your party. then talk to the girl in Castelia City which gives you seen data for Zorua. (Just go around the city, it won't take long.) to get a fateful encounter Celebi.
No, it is not possible to do the event in HeartGold and SoulSilver with any Celebi because the game reads what is encoded in Celebi's summary. You need a Celebi with a "Fateful Encounter" flag on it (this flag will be shown in its summary) in order to unlock the event in HeartGold and SoulSilver.
A Pokemon from a Diamond, Pearl, Platinum, Heartgold, or Soulsilver event.
Go to cheatcodes.com.
Zorua can be found in Castelia City by event with fateful encounter Celebi.
Yes you can get a Gracidea Flower from the lady in Floaroma Town with a Shaymin that you have received in a trade just as long as it has a fateful encounter flag on it and you can only get a Gracidea Flower in Pokémon Platinum, HeartGold and SoulSilver.