The official Pokémon Black and White Version 2 website has revealed that Keldeo will be distributed again to players of B2W2 via the Nintendo Wi-Fi Connection from January 25th to February 12th, 2013. Keldeo was previously distributed at gaming store locations around the world in the summer of 2012.

When players visit a field close to Floccesy Town with Keldeo in their party, Keldeo will be able to learn its signature move, Secret Sword. This will enable it to change from its Ordinary to its Resolute Form, thus gaining a new appearance. If the move is deleted or Keldeo is transferred back to Pokémon Black and White, it will revert to its Ordinary Form.

Press Release

Add the strength and resolve of the Mythical Pokémon Keldeo to your Pokémon Black Version 2 or Pokémon White Version 2 game in a special distribution event via Nintendo® Wi-Fi Connection! Keldeo will be available from January 25th to February 12th, 2013. This powerful Keldeo will know the moves Sacred Sword, Hydro Pump, Aqua Jet, and Swords Dance.

Once you have Keldeo in your party, complete an in-game event that will teach Keldeo its signature Secret Sword move and reveal a new Form for the Pokémon! Get all the details on how to change Keldeo into its Resolute Form.

Remember, Keldeo is available only from January 25th to February 12th, 2013 so don’t miss this chance to get this awesome Pokémon!

Source: http://www.pokemonblackwhite.com/pokemon-black-and-white-2/#en-us/pokemon/keldeo/details-keldeo-distribution