How about you use glow stone and arrange it in a circle with one log in the center. You set the log on fire and put a beacon block. During the exact middle of the day, if activated at the same time, the beacon will shoot up a beam to the high sun at his peak. Then, a glowing and bright figure will fly down and shoot lightning bolts and beams of light towards you. Then, when you get it down to half health, he will begin to pursue you and will not take damage. When he finally catches up to you, he will either do 5 hearts damage or you can lead him into water and he will be weakened. Then, you finish him off and the light figure will have a glowing, repulsing aura.
