When you get to Synda (The Black Dragon at end of game)there are two parts of the battle...one in her castle and the other in the Dark Realm. The Dark Realm Is harder because when you get to where Synda is...after her health is down to The "red" bar you change "Camra Viewpoint" and you have to use a new power. Then,when her health is down you can use your fury. Before that do A LOT of Dodging.You try to dodge her attacks while you are trying to attack her at the same time.
After you beat the game you go back to the swamp and restart with all of your powers...except for the new one.