I'm not sure if Arceus was confirmed or not. Hold on, let me look it up really quick.
EDIT: According to Serebii.net, there's an Arceus event for the games. You can trade your own over from Diamond, Pearl, or Platinum and it triggers an in-game event. You take the Arceus to Cynthia in a specific area (yet to be confirmed) and she will give you an option to take one of three Pokemon. Dialga, Palkia, or Giratina for you to keep. Each of these Pokemon stand at Level 1.
Again, I got this information from Serebii.net. Just restated in my own words.
Other than that, I'm not sure of anything else. You can ask Jordzz later. He probably would know more than myself.
