"Visit participating Walmart stores in the U.S. to find specially marked Pokémon Black Version 2 and Pokémon White Version 2 games. Inside each box you’ll find a code for one of three Sinnoh Pokémon: Turtwig, Chimchar, or Piplup! Beginning Trainers in the Sinnoh region get to pick one of these three as their first Pokémon, and now you can enter the code on the Pokémon Global Link promotions page to choose your favorite!
You won’t find these cool Pokémon in the wilds of Unova, so don’t miss your chance to get them here! What’s more, these Pokémon have special Abilities, making them different from any of the Pokémon you could transfer in from previous games. Quantities are limited, so visit Walmart stores to find these Pokémon Black Version 2 and Pokémon White Version 2 games today!"
"Get a Special Sinnoh Pokémon! Promotion period 12-06-2012 17:00 — 07-31-2013 17:58 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Did you get a specially marked copy of Pokémon Black Version 2 or Pokémon White Version 2 from a participating Walmart store? Did it have a code for one of the Sinnoh Pokémon? Here's your chance to enter that code and get Turtwig, Chimchar, or Piplup! Choose carefully—after you enter the code and befriend one of these Pokémon, you can't change your decision! The next time you use Game Sync, the Pokémon you choose will be transferred to your Pokémon Black Version 2 or Pokémon White Version 2 game. • You can get one Pokémon for each Game Sync ID registered to your PGL account."
— Pokémon Global Link
"Help! Help! They've destroyed my cousin's brain!! Oh, my god! They've already milked you, haven't they?!!" -- Phoncible P. Bone
There is a special marking on the outside, it looks blue on white 2 and orange/red on black 2. It shows all three starters and informs you the code inside allows you to pick the starter of your choice with an Internet connection and account.
It honestly isn't really worth it, the hidden abilities are the only thing that make them stand out, especially Chimchar's. I brought all the starters to my gold version then to white and on to black 2