id say the strat that worked for me when he was maxed hp was alwas wait for him to attack and take your time (except master mode) and use flurry ruses as damage typically 1 handed weapons and a shield its not worth using your bow or parrying as that leaves you open so he could dash toward you and get a hit in. In the second phase he gets electric weapons so if you can swap your weapons for wooden ones or guardian weapons ( guardian weapons do extra damage to guardian type enemies ) always have your shield up and get flurry's if your on full health he cant one shot you but he can do a parry move and swipe you with his sword that can one shot hope this helps!
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