Verified answer

You cant unless you trade in gts. It was a pokemon event for pokemon diamond pearl and platinum.

You can't. Arceus is an event-only Pokémon so there is no way to get it without cheats or trading with someone because its event was only available for a limited time for Pokémon Diamond and Pearl however it is no longer available.

i think it was a wifi event so u might not be able to get it anymore