There are 300 Pokemon in the Unova PokeDex in Black 2, right? So, how come my PokeDex says that I have seen 301 Pokemon? That makes no sense what so ever. Is it a glitch?
Have you seen Victini? While the numbers in the Unova Dex goes up to #300, Victini is #000, meaning there are 301 Pokemon in the Unova Dex.
Serebii - Unova Pokedex