How to Beat Nahyndri
The three siege weapons help tremendously during this fight.
Core difficulty, my party consisted of 6 characters (lvl 20) and 2 pets (Witch [Lich], Warpriest, Rogue, Fighter, Wizard, Shaman, Skeleton archer, Bismuth). I had various buffs, potions, scrolls etc. Every physcial dmg characters with attack 50+ and all magic dmg characters with huge spell penetration and masteries in their schools. I had like 25 summoned creatures to help.
Even when starting with Corrupt magic to dispel almost everything from the boss, he still remained with huge AC, healing and dmg.
My goons were able to get him to 40% top and then he just wiped everyone. I thought my witch with Absolute death spells will kill him – but to no avail, after 50% he just got some immunity to my spells (that healed him instead). Half of the spawned creatures were wiped by his AOEs or just fell into his summoned pits.
I was kinda clueless how to defeat him, because my party literaly could not get stronger at this point.
And then I noticed there are some ballistas (1 right from the heart, 2 on the left of the heart). I tried to use them and DUH – if you shot from it, it will deal direct 250 damage to the boss and it will stun him for 10 SECONDS. He will have his AC significantly lowered so you can actually hit him. As was said, there are 3 ballistas in total so you get 30 seconds of stun on the boss which should be way more than enough to trash him. Also while in stun, the boss was no longer immune to my negative energy spells so a few Absolute deaths just wrecked him.
Still, his story is really sad. Hope this will help someone struggling here.