This one will be a Nintendo WFC Event. So get your Mystery Gifts ready. August 3rd 2009 to September 13th 2009, that's how long it will last. You will get the Membership Card which allows you to enter the originally closed Canalave Inn. There you will fall asleep and land on New Moon Island. Your opponent will be a Lvl. 50 Darkrai.
Europeans, the Darkrai Event WILL be available in Europe in 2009. The exact date of release is still unknown though.