If you have an event Celebi in your Heart Gold/Soul Silver games, you will be able to trade it over to your copy of Black/White and receive the Zorua Pokemon. Simply go to one of Castelia City's gates. If you're at the right one, there will be a girl standing inside next to a Pokemon. When you talk to the girl with Celebi in your party, Celebi will pop out of it's Pokeball and Zorua will change from it's Illusion. After this time, you will be given Zorua as a gift. Enjoy it if you can get it!
Added by: Forgoten_Scars Mar 7th 2011, ID#15350