You have to beat the whole game. [or trade with somone who has one]
In sapphire you cant catch it without events or cheats:-)
hall of origin
The answer can easily be found in Where do you catch arceus
without cheats,you need to receive the oak's letter in the Nintendo event
You cannot catch shaymin on platinum without cheats unless u get the event xcard from toys r us
If you mean Arceus, you will have to blow the Azure Flute, which you get only by Mysterious Gift or you can use cheats (Action Replay), on the Spear Pillar, found at the top of Mt. Coronet.
you dont
Trade from Diamond, Pearl, or Platinum
You can't catch Arceus without cheats.. You can get it when an event is going on about Arceus..
It's impossible to catch one without cheats.
You can't.
no you cant