1. Make sure that the item you want to duplicate is exactly one, like a medicine.
2. Enter a battle.
3. In the first round, have Rudy use an item, such as a power apple.
4. Have Jack switch the position of the power apple and medicine (or whatever item you want to duplicate).
5. Have Cecilla defend.
6. In the second round, have Rudy use the power apple again. You will see that the medicine is gone.
7. Have Jack switch back the position of the power apple with the medicine (now an empty space).
7. Have Cecilia defend.
8. In the empty space where the medicine used to be there should be 255 medicines.