Q&A for How to Catch Uxie, Mesprit, and Azelf in Pokémon Black 2 and White 2

No, if you saved after they fainted, you will lose the opportunity. However, if you saved before the battle, you can perform a soft reset to attempt catching them again.

Unfortunately, if you defeat Mesprit, you cannot re-encounter it in Pokémon Black 2 or White 2. For future legendary encounters, save your game before the battle; if you accidentally defeat the Pokémon, you can reset your console to try again.

Yes, if you run out of Poké Balls during the encounter, you cannot re-battle them. It is wise to ensure you have a sufficient supply of Poké Balls before starting the battle.

Catching Uxie, Mesprit, and Azelf primarily updates your Pokédex entries. Afterward, you can show your Pokédex to Professor Juniper in Nuvema Town to receive TMs for Protect and False Swipe. If you complete the entire Unova Pokédex, show it to the game director at the Game Freak building in Castelia City to earn a completion certificate.

No, Zekrom is exclusive to Pokémon Black 2; in White 2, you will catch Reshiram instead. However, you can catch Uxie, Mesprit, and Azelf in both game versions.