The Medal Rally is a new feature in Black 2 and White 2 that acts as an in-game achievement system. There are over 200 medals to collect, ranging from simple tasks like walking a certain number of steps to more challenging feats like winning a specific number of battles at the Pokémon World Tournament or catching every Pokémon in the Unova Pokédex. You can view your collected medals and receive new ones from the Medal Box guy in any Pokémon Center.
Collecting medals is a fun way to track your progress and provides additional goals beyond the main story. Some medals are awarded for reaching certain milestones, while others require specific actions or exploration. For example, you can get medals for visiting every town, using every HM, or even for having a Pokémon faint a certain number of times. While they don't offer direct gameplay advantages, they provide a sense of accomplishment and extend the replayability of the game. Aim to collect as many as you can to truly master the Unova region!