Being level 17 is enough to survive Zephyros' charge-up attack indefinitely(with enough potions), but he heals for 500 when he's near death.
Is it possible to kill him at the Black Citadel?
Being level 17 is enough to survive Zephyros' charge-up attack indefinitely(with enough potions), but he heals for 500 when he's near death.
Is it possible to kill him at the Black Citadel?
Yes, but you have to lose to do so. I won't give any spoilers. Die on purpose and you'll win at the Black Citadel.
In your first battle with him, you need to use your special power that you acquire after a certain event happens during that battle (It's a potential spoiler, but it's pretty obvious when it happens). Using that special power should end the battle, if I remember correctly.
I would assume that it is possible, there is an achievement called "Hero" which requires the player to defeat Zephyros. They would not release a game on steam where the achievements are impossible to get.