Instructions
Equip an empty bottle in your main hand. Wait for the cut scene to finish.
Swing your bottle at the energy spheres that Ganondorf shoots at you. If your timing is right, you'll knock the spheres back at your enemy. He'll try to deflect it back at you, making a kind of video ping-pong. Eventually, one of the spheres will strike him, and he'll be momentarily stunned.
Shoot your Light Arrow at him and he'll fall to the floor. Run over to Ganondorf and strike him as many times as you can.
Repeat the swing/shoot/strike combo a few times and down he goes.