Here are the steps on how to duplicate Pokemon and items:
Duplicating Pokémon
1. Catch a Pokémon that you want to duplicate.
2. Save the game.
3. Turn the game off.
4. Take out the Pokémon from its Poké Ball slot.
5. Replace the Pokémon in the Poké Ball slot with a different Pokémon.
6. Turn the game back on and load the saved game.
7. The original Pokémon will still be in your PC, and the new one will be in the Poké Ball slot.
8. Repeat steps 3-7 as many times as you want to duplicate the Pokémon.
Duplicating items
1. Get the items that you want to duplicate.
2. Save the game.
3. Turn the game off.
4. Take out the items from the bag.
5. Replace the items in the bag with different items.
6. Turn the game back on and load the saved game.
7. The original items will still be in the bag, and the new ones will be there too.
8. Repeat steps 3-7 as many times as you want to duplicate the items.