The Ancient Wyvern boss fight is really not much of a boss fight at all. Instead, you will simply be fighting your way through hordes of serpent men, until you can successfully hit the Wyvern one time, ending the fight. When the fight begins you will want to charge forward through the Wyvern’s legs and immediately head left into the building. Try to get to the side and avoid the Wyvern’s fire breath attack, while taking out the 3 enemies there. Next head forward and then right. 2 Serpent men will drop from the ceiling. Take care of them and proceed up the stairs. There are 2 more serpent men here, kill them and then sprint across the narrow bridgelike path, avoiding the fireballs, serpent men and Wyvern’s breath. You are not trying to kill anything else now, just make for the ladder dead ahead on the left. Climb it as fast as you can, and wait for the Wyvern’s fire to pass. Then head out onto the platform, drop down onto a large stone column and wait for the Wyvern to dip his head. Run, jump and plunge attack his face for the Victory. .
As found on Youtube