How to get Latias or Latios in Pokemon Black and White 2

                   

                    First of all, you need to have a master-ball. After that, head to Striaton city. Then, exit there and head towards the Dream yard. Once you get to the Dream yard, either Latias or Latios will pop up. If you are on Black 2, Latios will come. If you are on White 2, Latias will come. If you wander around the Dream yard, Latias or Latios will fly around above you. Eventually, they will stop flying and soon they will challenge you to a battle. Use your master-ball and soon you will have successfully caught Latias or Latios! Well, good luck getting Latias or Latios!