'Pokémon the Movie: White—Victini and Zekrom' and 'Pokémon the Movie: Black—Victini and Reshiram' are coming to the theaters. To commemorate this, you can now get the Victory Pokémon, Victini! Here's an extract from the Official Pokémon Site:
First, this Level 50 Victini knows the move V-create, an immensely powerful Fire-type move that also lowers Victini’s Defense, Special Defense, and Speed. Then, it knows the Searing Shot move, another strong Fire-type attack that hits all other Pokémon in a Double Battle. To cap it off, this Victini knows the signature moves of both Reshiram and Zekrom: Fusion Flare and Fusion Bolt! Victini is also holding a Fire Gem, which provides a one-time power boost to one of Victini's Fire-type moves.
To get this Pokémon, it's simple. All you have to do is start up your Pokémon Black or White game and select Mystery Gift from the main menu. First, make sure you have less than 12 Wonder Cards. You will have to delete one if you do. Select 'Get via Nintendo WFC' from the 'Receive Gift' menu. After that, it should come in quite fine. After that, you just need to get it from the delivery man at the Pokémon Center. He gives you the Pokémon itself, so make sure you have a free space in your party.

The event has been open since December 3rd. Don't take too long to get it, though. The event will end on December 31st.