Sorry. It's impossible.
It is an amazing legendary pokemon.
by apokemon event or trade
get all the badges and then you can find him get all the badges and then you can find him
There's only 1 way. You need the Arseus flute, which can be obtained by a event of action replay. Next climb up to mt. conoret again, and stay on the triangle where Dialga once stood. The flute will play from itself, and a staircase will open. Walk up the staircase and Arseus will be up there. He'll be lvl 80
Arceus obiously
Special Events, You get a Ticket to Unlock extra areas. These are usually one time events, So If you missed the events, You will have to Trade without People, Or Obtain one through an Action Replay.
cheat and get azure flute then go to mount cornet summit and blow the flute
I don't know if this answers your question but it came out with sinno, Diamond and Pearl.
You need the Azure Flute from Wi-Fi Mystery Gift. Unavailable anymore.
Arceus is, inthe Pokemon world, the Pokemon who created the world. He is the last on the pokedex, 493, and has the ability Multitype
Use a game shark or an ar, cause there is curently no way to aquire Arceus without cheats.