It is an event in the new Pokémon Black & White games that gives you the chance to catch Zoroark. To activate this event, however, one of the three Shiny Legendary Beasts Entei, Raikou or Suicune are necessary. You can obtain them by pre-ordering tickets for the 13th movie Phantom Champion: Zoroark.
To unlock the event you have to have a shiny Entei , Raikou or Suicune transferred to your Black White versions. The download will be available in Japan from 18th June till August 31st. Also at Gamestops in March and April of 2011.
Take your event shiny pokemon listed above to Lostlorn Forest, and you’ll see a pokemon that looks like a legendary that actually turns into Zoroark when you engage it.