what you have to do is get the heart scale cheat, which gives you 493 heart scales, then you hold L&R and you walk and you should run into an arceus, so you look at the national dex, check what entr he is, throw away heart scales until you get to it's number, hold L&R again, and you should find it.
P.S. you must walk through a patch of grass or any other place that you may run into Pokemon
your answer and more for AR codes... @ Neoseeker.com
Action replay
Action replay is not an Pokémon item that can be obtained in Diamond.
You can use certain AR codes to get Kyogre in your party, or get a Pokemon Modifier code.
Go to neoseekers.com
No
no you have to get is from an action replay or go to a Pokemon event
action replay
action replay
action replay
action replay
its a cheat