>In Pokémon Black and White, Professor Cedric Juniper upgrades the player's Pokédex to the National mode when the player first leaves his/her own house after defeating N and Ghetsis. As with previous generations, event Pokémon including Keldeo, Meloetta and Genesect are not needed to complete the National Pokédex.
Source: Bulbapedia/ PokeDex
Victini is an event Pokemon, so he is not needed.
