If you wander into Numara Atoll in disc 2, the chances of winning are low but possible. Recommend Seal/Lucky 0 Magic Damage, Poison, Double, Blind, as well as plenty of Angel's Plume. If you make use of magic, it's not a problem to damage them. They just have WAY too much HP, and absolutely vicious attacks. All-Aquaus, for example, can do 2,000 damage to all characters if you're around level 25. If you return on disc 4 or so, you should be able to handle them. -- though it may still take a couple of turns.