Castlevania Lords of Shadow last boss

I read this here

Satan can use both Shadow Magic and Light Magic, and the crux of the battle revolves around your own ability to use those same attacks. Don't worry about your magic meters, as they will never decrease, meaning that you have an unlimited amount of magic to use in the fight. And this magic is the key, since you'll need to attack Satan with the opposite magic he's currently invoking in order to have any hope of actually damaging him. Dont bother using standard attacks as they will never damage him. When the staff he wields glows red, it means he has Shadow Magic engaged, so use Light Magic attacks with your Combat Cross to start to damage him. Likewise, if his staff glows blue, he's using Light Magic, at which point you'll want to invoke Shadow Magic to eliminate him

Based on this I am guessing that you probably hit him with standard attacks or with the same type of magic.

EDIT:
When he's stunned, you can initiate quicktime events to damage him and ultimately finish him off, but remember to navigate the runes that surround him once stunned using your own magic, or you'll never get to him in one piece.