When you face him, he 1. has poor accuracy, any decent dodger can avoid him. 2. such poor attack power that A mage who is fortified (and you get such a staff in this chapter before the 2nd 2 Garnef clones...) can take 0 damage from him (and very little without the buff anyways).
God was a dream of good government. You will soon have your God, and you will make it with your own hands.-Morpheus -Deus Ex
My marth walked up to Medeus, and was doing an insane amount of damage with falchion, on top of attacking twice. I attack, he misses, I kill. Boss dead, pretty lame. Gharnizzle was also kind of lame, seeing as how finding the right one was annoying, but after that he doesn't last very long.