In the world of Pokémon, you go into tall grass to search for new creatures in the wild. In the real world ... GameStop. From March 4 to March 24, you can bring your DS and your copy of Pokémon Black, White, Black 2, or White 2 into a participating store to receive Meloetta, a Melody Pokémon who can change Formes mid-fight, using a move learned at Café Sonata in Castelia City.
To learn more about Meloetta, you can see the "Meloetta's Moonlight Serenade" short through the mobile Pokémon TV app. We're reasonably certain that's the only time we're going to refer you to a cartoon for information. We're not making any promises.