Hey guys, I found this fight to be pretty easy once you know how the fight actually works. Should be noted that I did the fight on New Game ++
The Keeper has 4 segments of health you need to take down in order to kill it. To even start to do actual damage you must first take down its stamina meter (yellowish orange bar under the health bars) DO NOT TAKE THEM DOWN FULLY OR YOU WILL BE ONE SHOT KILLED BY A MAGIC EXPLOSION. Instead what you need to do is get the meter down to almost nothing then the boss will panic and begin looking around, which is where you take the opportunity to run behind the wall he errects and stand close to it (continuously sucks your health so keep potions at the ready) He uses the wall to suck pieces off of it for some reason which raises his stamina back up fully if you do not stand behind it as previously mentioned. Every time you do this he will explode for some reason and lose an entire health segment( only has FOUR). Do not exit from behind the wall until it lowers on its own, then simply repeat the process till you remove THREE health segments and when hes on his last health bar you can just run up to him and smash his face in like a traditional boss. DONE!
For visual aid heres a video I made of how I killed him on New Game++