sorry for late reply in comments but it only works if you have it equipped and attack lindamea with it. all i did was reset when i got the line and same as the other.
This fucker died from fire + poison + rupture + blood loss the second when the field effect was out. I also died because he oneshot my full health bar. I lost. It's a draw but the game didn't let me.
i might explain wrong but. your suppose to outlast lindamea. the immortality buff lasts 20 turns or so the turn count goes down either you or lindamea turn it keeps ticking down. try guardian angel,evasion with windless wrap or upon the last turn use something like requiem or stack defense buffs.
(Late) A good trick is going to the fight with less than 2400,but more than 1200 speed,and having the Great Sword,that halves your speed.Then once phase 3 starts,equip the sword,and the next turn unequip it,and that makes the counter go away in Lindamea's turn,killing him
