First of all: Cynthia doesn't have an Arceus at all...
Now to your question:
Action Replay Ds/Dsi > Pokemon Diamond /Pearl or Platinum codes > Event Modifier Codes > Azareus
Press L&R, go into a mart, talk to the green guy and go to spear pillar.
Im German so sry for mistakes ;)
You can replay the arceus event with action replay.
you can not get arceus with no action replay
You cannot get one yet without an Action Replay.
Trade.
Action Replay yourself a Master Ball.
you cant do that you have to use action replay
you need an code for action replay to get arceus but its super long search it on google it may tell you
No,but their is a way to get shiny arceus
Action Replay.
No
Use action replay
use action replay