Pokémon Black/White have a new “ethereal”-class legendary, similar to Mew or Celebi, in the form of Victini, who’s curiously #000 in the Pokédex. As with all ethereal legendaries, there’s a trick to acquiring Victini.
When Pokémon Black/White release this March 6th, you’ll be able to take the games online to download the Liberty Pass item off Nintendo Wi-Fi from March 6th – April 10th. The Liberty Pass will allow you to hop aboard a ship in Castelia (Hiun) City and sale to Liberty Island, which is where you can find Victini.
Victini is a Fire/Psychic type, and comes with the Victory Star ability, which allows it to increase the accuracy of all the Pokémon in your party.