all you need to do is catch darkrai shaymin and crescellia and then show them to professor oak then he will tell you to catch the 3 trio mespirit azelf and uxie the after you catch it show it to him and he will show you a secret tunnel located in mount coronet then the tunnel leads to a weird islnad where averything is changing colors he says its is the rainbow island where he once met ho oh and you find out youre in kanto and suddenly a shadow that is arcues kidnaps oak then you have to recuse him on this peak in rainbow island you have to bike cuz its long like the path to shaymin then you battle arceaus after you catch or beat it a little orb appears and in that orb is oak then he and you went home.
You need arceus event
its not on a route, to find arceus you need action replay and go to mount coronet.Get to the end and you'll find steps.Keep going until you find arceus at the end of them.
you need a arceus then go to the ruins of alpha. if you do not have a arceus then your out of luck.
you cant u need a Nintendo event that u physically have to be at to receive arceus
you can find arceus in the hoenn region.
You will need the Mysyery gift azure flute. Once you have it, go to the spear pillar where you found Dialga/Palkia and use it. There will be a LONG stairway and on top of it you will find Arceus waiting for you.
Where ever you find normal Arceus. :p
You'll need to trade from the Pokemon HeartGold, Diamond, Pearl, and Platinum.
Ice/fire/rock/water/eletrick or physic arceus
You can not FIND arceus in a city. You must find it through the evnt for Pearl Daimond or Platinum.
you dont need codes for arceus!for more info ask "how do you get arceus by using ar"
you cant find arceus in Pokemon heart gold you need to transfer it over from Pokemon diamond or pearl . you can find it in the hall of origin if you have a azure flute you go to the spear pillar and you will see him at level 80 so be prepared