Arceus is a mythical Pokémon that is not found in the wild in the game. It can only be obtained through specific events or by transferring it from other games.
Here are some ways you could potentially get Arceus:
* Events: In the past, there were events where players could receive Arceus. However, these events are no longer active.
* Trading: If you know someone who has Arceus, you could potentially trade for it.
* Transferring: You can transfer Arceus from Pokémon Diamond, Pearl, or Platinum to HeartGold using the Pal Park. However, you would need to have obtained Arceus in those games previously.
While it's possible to obtain Arceus in other ways, it is not possible to obtain it through regular gameplay in Pokémon HeartGold.