While I don't remember all the aspects of this boss and don't know if the following advise for some reason is horrible for that battle: When in doubt, bring the Sentinel out. I only learned about the true benefits of a Sentinel against bosses very late in the game. Off the top of my head, I only remember finding it necessary to apply Sentinel stance against some Eidolons and Attacus. But I also found good use for it in battles against Oretoises and the likes. But yeah, my point is, against bosses a Sentinel can help you last through a long fight. You just need more patience, but it's the safest way to go. Make sure to keep the Sentinel alive and gradually wear down the boss till it says "FUCK THIS SHIT!" and drops the controller on the floor... Or you know, dies.