Preparations for the Curse
The confrontation with Nyrissa can be incredibly easy or a bit of a brawl, depending on your past actions. More important, however, is what happens after the fight. We won’t spoil it for you, suffice to say that depending on how mouthy you are, there could be a bit more gameplay left. If you want to squeeze every bit of combat and content out of this game, or if your character just doesn’t know when to leave well enough alone, you might want to consider making some preparations now that’ll help you out in the long-run.
First, recruit mercenaries from Anoriel. Casters are not going to be very helpful in the future, so get warriors, ideally four melee characters and two ranged characters. A Monk and Paladin are fairly useful given the former’s low gear requirements (just slap on gear that boosts Wisdom, Dexterity, Strength and/or Constitution - your casters won’t be needing it anymore - Rings of Protection and the like and you’re good) and their potential ability to use Restoration, while the latter’s ability to fight and heal via channeling positive energy is also welcome. Be sure to sell off every bit of junk you can, retaining gear for your new warriors and any potions and scrolls you have. You’ll need the money.
Making these preparations now can spare you a lot of grief later on.
When you’re ready, make your way to the second floor and head to the locked door in the hallway that runs the length of the level. If you possess all three keys, the door should open when you try it. Spellbuff generously and head through the door to find the Horned Hunter waiting for you. Avoid an unnecessary confrontation with him for now, after which Nyrissa will show up and you’ll be presented with a variety of options for deal with her.
Most of them lead to conflict, bit if you romanced her earlier the following option should be available: "I’m not here to kill you - but to stop you. And heal you, if there’s any hope of that.". If you wish to avoid a fight, pick that dialogue option followed by "Evil only begets more evil, but there must be a way to stop it. Trust me. Stop. A battle will not solve or help anything." Picking these options will convince Nyrissa to yield, sparing you a fight. Any other responses will have to be backed up with violence.
Nyrissa’s a bit of an odd foe, as her ridiculously high Armor Class of 51 makes landing physical blows difficult. It’s not outside the range of an incredibly well-built warrior who, with flanking and spell-buffs can probably hit her around 50% of the time with their primary attack, but it’s still fair enough protection from physical damage on its own. On top of this she’s boasts just over 500 Hit Points and Damage Reduction 10/slashing, which shouldn’t slow you down by much anymore.
Her spell defenses - or lack thereof - is even more bizarre. She has no Spell Resistance and no immunities, only incredibly high Reflex and Will Saves and a decent Fortitude Save. A well-built caster can probably hit her with Baleful Polymorph around 10% of the time, which isn’t good odds, but against the final boss it’s… well, not a bad option, really. Finger of Death and Destruction are more likely to work due to their higher level, and a high level caster can deal significant damage to her with a single successful casting, and come away with consolation damage if she passes her save.
Focus your casters on using the aforementioned spells to target her Fortitude Save while your warriors attack Nyrissa when they can, and when she summons allies. These include Owlbear-like Treants and Wyvern-like Treants who are moderately powerful combatants in their own right, possessing over 250 Hit Points, Damage Reduction 10/Cold Iron and a high enough Attack Bonus to threaten your warriors, although not high enough to guarantee hits. Later on she’ll summon a Yellow Dweomerwyvern, Green Dweomerwyvern and Red Dweomerbear followed by a Black Dweomerbear, a Quickadon and another Green Dweomerwyvern… enough to keep your warriors quite busy.
Nyrissa for her part will cast offensive spells when she’s not summoning allies, including Wail of the Banshee, Tsunami, Irresistible Charm, Phantasmal Slaughter, Death Clutch, Vinetrap, Finger of Death after which she’ll busy herself with endless Rays of Annihilation, which deals 20d6 divine damage if she succeeds at a ranged touch attack. She’s also capable of teleporting about and protecting herself with Shield and Seamantle and spamming a pair of Heal spells in quick succession, which she’ll do reliably after her health falls to around 2/3rds of her maximum. She seems restricted to doing this only several times, but… that’s a lot of progress she can erase, making a permanent debilitation like Baleful Polymorph even more appealing.
Given the nature of Nyrissa’s offense, you’ll want to spread Death Ward and Mind Blank around as liberally as possible. Naturally having plenty of Heal (or better yet, Mass Heal) spells will help keep your characters fighting fit, and Break Enchantment will hopefully help characters who have been affected by Irresistible Charm or Hold Monster.
Defeat Nyrissa and you’ll find yourself in a bit of dialogue, provided with several options for dealing with your vanquished foe. If you didn’t romance her earlier, giving her the Briar won’t do any good and she’ll end up rejecting your offer, no matter what option you pick after that. If you pick [Let Nyrissa go] or [Finish Nyrissa] you can watch the scene that follows, and when the Horned Hunter speaks to you again simply say "Who are you?" for another revelation. Afterwards you can enter the portal the Horned Hunter creates and watch the end of the game, including a recap of your actions and their post-game effects.
On the other hand, if you pick the option [Offer Nyrissa an alliance] followed by "I don’t like when 'rules' are imposed on me. My offer still stands.", or if after dealing with Nyrissa you attack the Horned Hunter when he speaks to you, the Lantern King will take offense at you spoiling his fun and swears to "repay you with your own coin." In this case going through the portal won’t end the game, but start the next chapter…
Warning!: Before going through the Lantern King’s portal you should make sure you’ve completed the preparations suggested under the "Preparations for the Curse" header. Doing so now may save you a bit of grief going forward.