Where do you find Darkrai in Pokemon Platinum?

Okay so you must have a action replay!Then you put in the walk through walls code.Then go to the sailor's house in Canalave city.Talk to the mom.Then sail to Fullmoon isle.Go into the place where you find Cresselia.Then you go through those trees with the cheat code.Go North,then you'll find a level 40 Darkrai.Make sure you save!