GEOSGAENO
HP: 32767

STRATEGY: This battle is easy just with a simple element of preparation. Before battle equip everyone with armour that protects against petrification. Stone Ward can easily be added to armour if you have at least 5 softs.
This monster has high defence, and Armour Break is useless, so attack with weapons which have piercing abilities. Cast Hastega at the start, and protect if needed. Then hit him with everything you've got. Attack Reels is very useful in this fight. Use Al Bhed Potions to heal.
If you're lucky, you will get a piece of armour with the No Encounters ability added. You can also get this with weapons.