Cagnazzo's probably the easiest boss in the game, if you know what you're doing. Give Yang two Thunder Claws, equip Cecil with the Legend Sword, because it has more attack power than the Ancient Sword, have Porom heal, and have Palom and Tellah use Bolt 2 and Bolt 3 respectively. To remedy his Tsunami attack, simply attack him with a Bolt spell while his wave barrier is up.