Boss Battle: Shrieker

As seems to have become standard in the first two Final Fantasies, reaching the Shrieker is more difficult than defeating him. Before leaving for Kas'ion I recommend picking up another Cure scroll. You'll see why. You'll also need 400 gil to pay Cid for an airship ride down to the castle.

Seconds after you enter Kas'ion you'll meet Gordon skulking the shadows of a stairwell. He came to retrieve the Sunfire but couldn't handle the castle's baddies. (Weenie). He's more than happy to join you, though, and you should feel free to use that extra Cure scroll to add another healer to your party. :)

Soldier on until you reach the Shrieker.

Your first few turns agains the Shrieker may cause you some anxiety. He absorbs all spells cast at him (and I mean all; he will gain life if you try to cast sleep, for instance, not just from damage spells) and he casts medium level versions of fire, ice, and bolt that will do a decent amount of damage to your entire group. Fortunately his shriek is more dangerous than his bite. Cast cure on your party members as often as necessary to survive the first five to six turns and the Shrieker will run out of mana. Reduced to meager physical attacks it becomes a game of endurance, and you have four to one odds. Wail away at him, trying as best as able to ignore the meager amounts of damage you're doing per hit, and eventually he will die. It might take five or six minutes, just fyi.