The final battle with the demon king himself. The first phase is fairly simple; he'll block all of your attacks no matter what unless you're lucky enough to land a hit or two before he retaliates. When you shield bash his slashes and attack one time (only once) he'll slash again, and if you do this four times in a row he'll fall and allow you to slash him up. After a few hits, he'll call a lightning storm to supercharge his blade. In this phase, he'll use electric skyward strikes to attack you from afar and also will charge into your face. The way to attack him is to steal his thunder (literally) by raising your sword when the lightning strikes and swinging it back at him to stun him. After a few hits, he'll fall on his back; perform a finishing strike to deliver the final blow. It usually misses the first time.
After the battle, he'll make an allusion to a certain villain in future games..and is then sealed into the Master Sword.