If you want to fight Ozma, you don't really need the Pumice Piece.
Egoist's Armlet nullifies Shadow elemental damage.
Ninja Gear absorbs Shadow.
Demon's mail absorbs Shadow.
Chimaera Armlet nullifies Holy.
That will help certain parties out against Ozma. If you don't want to fight him, though, you definitely don't need the pumice piece. Take the Tin Armour. It's great.
