I AM NOT RESPONSIBLE FOR THE LOSS OF ANY ITEMS, YOUR WORLD BEING CORRUPTED, YOUR CAT DYING, OR GLOBAL WARMING!
Duplicating will make the game a lot less fun, I suggest to do it at your own caution.
You have been warned.
To start you will need:
- An account with Xbox Live
- A friend with Xbox Live
- The items you wish to duplicate
- Auto-save disabled
- Join the friend's game and save and exit to the menu.
- Join back and put the items you wish to duplicate into a chest, then exit to the menu WITHOUT saving.
- Join back again and check the chest, you should now have double the items.
Albeit more difficult, you need:
- A storage device other than the one you use now (cloud is fine)
- Put all the stuff you want to duplicate into a chest in any world you have.
- Save and exit to the menu.
- Press the guide button and navigate over to the 'settings' tab and go to 'system settings'.
- Select 'storage'.
- Go to the storage device that has your terraria save in it.
- Open your terraria save and copy both your 'world' and 'character' saves to another device.
- Start up Terraria and select the device you just copied your saves on.
- Go to the world that has the items you wish to duplicate and put them into your inventory, then save the game.
- Complete steps 3-5 again, except going to the second device.
- Now copy the 'character' save (AND ONLY THE CHARACTER SAVE) back to your original device.
- Start up Terraria and select the original device.
- You should now have the items in both your inventory and the chest.
I wish you the best of luck!