Q&A for How to Catch Reshiram and Zekrom in Pokémon Omega Ruby and Alpha Sapphire

You can battle it again after defeating the Elite Four.

Reshiram has a low catch rate, so you will need to be persistent. Even if you exhaust your Ultra Balls, a standard Poké Ball can still be effective.

After dealing with Groudon/Kyogre and defeating the Elite Four, go to the top of Meteor Falls to meet Zinnia who will give you directions to get your Rayquaza.

In Pokémon Omega Ruby and Alpha Sapphire, you cannot obtain additional Master Balls through normal gameplay. Item duplication glitches for Master Balls were exclusive to the original Ruby, Sapphire, and Emerald versions.

Yes, you will need both Reshiram and Zekrom. With both Pokémon in your party, a new area called the Gnarled Den will become accessible behind Mt. Chimney, where you can find Kyurem.

You can encounter Zekrom or Reshiram only once.

You can still acquire the Reshiram from this event, even if you already possess one obtained through a trade or from a previous game.