What is the Arceus code th re-battle him in Pokemon diamond?

To re-battle arceus there is only two ways! use the modifier code on Action Replay.

Or before you battle Arceus for your first time save it right in front of him and then battle him if you don't catch him and he loses his HP turn the game off, then turn it back on and you re-battle him! WARNING: If don't catch him the first time you battle him...when you turn off the game and turn it back on you'll still be in front of Arceus but the first time you battle him wouldn't count so I'd try to catch him on my first time...ut remember if you save it in front of him before you battle it you have plenty more chances of catching it!