I'm not joking when I post this. It really works,try it! Have the master ball first in the pokeballs bag. Then, when you're in battle, use the master ball to snag on the first pokemon's turn. On the second pokemon's turn, use the Y button to switch the master ball from first to second. Attack, call, whatever with the second pokemon. After you use the master ball, check your bag. It's still there!(Works with any other type of pokeball too!)