Doomsday is the ultimate spell! You may think if you've got it that it's a waste of time because it damages your allies. Well for Zidane you just have to equip Ninja Gear. For Vivi you have to equip Shadow Armlet. Anyone else just equip Pumice Piece and another Shadow Armlet. Doomsday is better than the summon Ark which you get from pumice piece.