Get Darkrai in Pokémon Platinum

The complimentary Pokémon to Cresselia is available only from 3rd August 2009 to 3rd September 2009. Get it now before it goes forever!

Steps

After beating the Elite Four, get the National Pokedex from Professor Oak.
Awaken Sailor Edrith's son with Cresselia Lunar Wing.
Fly to Jubilife City.
Go to the TV Station. Speak to the manager on the third floor. Tell him "Everyone Happy, WiFi Connection.
Save your game and turn it off.
MYSTERY GIFT should appear on the Start Menu. Select it.
Choose "Receive Gift", then "Get via WiFi connection."
"Members' Card" will appear. Answer "yes" from the drop down menu.
The "Members' Card" will become available by speaking to a man in green at any of the Pokemarts.
Fly to Canalave City. You can now enter the Harbor Inn!
Go inside and talk to the man. He will say that he has been expecting you.
Save when you get to the Island. Go into the forest.
You will see Darkrai floating on the lake. Talk to it.
You will enter a battle with it. It is at Level 50.
Catch Darkrai and return to Canalave City.
When you return, save your game and resume play.

It will not be easy to capture; make sure you have a lot of Ultra Balls, Dusk Balls (if you plan to capture it at night) and Timer Balls.

This event is only available from 3rd August 2009 through to 3rd September 2009 on the Nintendo DS WiFi system.