No, you do not need to complete your Pokedex. You have to do a Wi-Fi event. However, all of the events regarding Arceus have already passed.
You can replay the arceus event with action replay.
If you mean soul silver, it is yet unknown you have to trade the event arceus to it to get giratina, dialga or palkia.
No, the movie Arceus that has been distributed in Japan is not the only Arceus that will work for the Heart Gold and Soul Silver Arceus event. That Arceus was special, because of the fact it unlocked a special Pichu event in Heart Gold and Soul Silver. Any Arceus will work for the event in which you can get a Level 1 Dialga, Palkia, or Giratina in Pokemon Heart Gold and Soul Silver.
you can't catch it, you have to get it from an event which has passed
You Can Get Arceus On Pokemon Soul Silver By Using A Cheat Cartridge, Trading It From Another Pokemon Game (Pokemon Diamond, Pearl Or Platinum) Or Via A Nintendo Event. Hope I Could Help =)
arceus is an event pokemon.
if its the arceus from Sinnoh then you will trigger the arceus event which is awesome
There used to be an event, but now, Arceus is impossible to obtain without the use of a glitch or cheating device.
there is not going to be an event for arceus on Pokemon black sorry to disapoint you.....!
You can only get Arceus by an Event.
Arceus is an event Pokemon and can only be obtained by an event.
A event which you can get palkia, dialga or giritina