1. Start up your game.
2. Go to Goldenrod City.
3. Enter the Goldenrod Game Corner and talk to the person in the back.
4. Go to the casino shop and talk to the women behind the counter.
5. Deposit all your items in the PC except the Master Ball.
6. Now buy a Poké Doll from the shop.
7. Use the Poké Doll on a female Pokemon.
8. Go back to the PC and hold the Master Ball.
9. Press Start and select “Pokemon” and then talk to the women again.
10. Deposit the Poké Doll and withdraw the Master Ball.
11. Repeat steps 7-10 as many times as desired to duplicate the Master Ball.