If you go to the battle tower in the battle frontier you can duplicate pokemon by first going to the pc in the lobby. Place up to six pokemon in a box then get of the computer, now save your game and get back on the computer. Withdraw your pokemon you deposited and talk to the receptionist closest to you. Enter at least one or more of the pokemon you deposited and the girl will ask to save your game. Say yes and when it says " do you want to save your game" say no. Now shut of the power and turn it back on. If you check your box all of the pokemon you deposited will now be in the pc and your party. You can also duplicate items like the master ball by giving it to your pokemon and then duplicate the pokemon. [Note that you can't duplicate Mewtwo, Lugia, Ho-oh, Kyogre, Groudon or Rayquaza.