Final Fantasy 2
Select "Item" and press A on an empty slot
during a battle. Move up until the equipment in that characters
left and right hands appears. Press A on the weapon to
be duplicated. Press B and complete the battle or retreat.
After the battle, equip that character with their weapon in the
same hand it was in. The weapon should have a "2" next
to it. Unequip, then re-equip the weapon. You should now have
one copy of the weapon equipped and another one in inventory.