K', so there are two ways to get Victini on Pokemon Black or White.
You can get it via Wi-Fi, by using the mystery gift option, which is going on now. You can also get the *Liberty Pass and board the yellow ship in Castila city.
Hope this Helps!!!!! (why is the writing green?!?!?)
*You are now unable to get the pass, or board the ship, unless you go back in time......