I've only got 3 potions which are my only health restoring items. When I get the boss's health down, he floats around in the air and spams a lightning attack which does huge damage and seems to be impossible to avoid. I've read that Slow Time helps, but I missed that spell. For me to get it, I would have to replay an earlier a level. But there is a glitch that wipes your achievement progress if you replay levels before completing the game. So it looks I'm screwed
Did you guys beat the boss without Slow Time? If so, how?