I did the boss battle with no upgrades other than the ones necessary for achievements the key to the fight is memorizing the moves the first part of the boss battle is harder than the second he has 2 moves and is wearing a coloured shield use that coloured move on him after he attacked you, as there is a small delay where you can attack him(he will also turn into a shadow where you will need to change dimensions) . After you beat him like that he turns into a giant monster whose attacks are much easier to read as they are all sound based or very obviously hinted to.