you needed to get it at the event ,or get some one who has it.arceus can't breed.
Arceas has to be caught in Pokemon diamond, pearl, or platinum, then traded to Soul-Silver and HeartGold.
darkrai arceas (with plate)
You have to trade it from Diamond, Platinum or Pearl
by-Pokeexpert980 The same as PEARL/DIAMOND/PLATNIUM 493
trade from platnium
Sorry no way to. Trade with diamond or pearl
the best way to get arceas in Pokemon diamond might be hard for you but i bet you'll think it was worth it! i have all the Pokemon on earth and arceas might have been the second hardest to get you have to get 3 dialga's and 3palkia's then put all of them in your party then they'll morph together then somehow they turn into one arceas!! i was as surprised you are!!! it may sound impossible but i speak the truth!!!!You can also you action replay which is a lot easier FROM FPM
in my view i would have to say arceas (with plate) and dark rai
in the national pokedex: arceas in the regular pokedex: dialga
NO THERE is no second map in diamond and pearl.(that includes platnium).
same place as diamond and pearl.
trade from pearl, diamond, or platnium