ITEM DUPLICATION
First make sure the item you want to duplicate is equipped, then enter a battle and select the Item option of the person with the item you wish to duplicate. Scroll down to a blank space on the item list and press A to place a glove there, scroll back up to the equipped items then press A on the one you'll be duplicating, then press B to leave the screen.
Hold the L and R buttons to run from the battle, press X to see the subscreen, select Equip and the character who has the item, press A on empty spot the item used to occupy, then press A on the actual item that's now in the items list. You will now see that your character has two of the selected item equipped.
WARNING: Using this little trick could prevent you from getting other items that you need to complete the game.
