Objective: Reach the Crown of Karsus and dominate or destroy the Absolute.
Hazards: Nautilus bombardments, dominated Red Dragon, unlimited illithid spawns.
Point of No Return: Taking the skiff to the Morphic Pool locks out the rest of the game permanently.
1. The Morphic Pool & The Brain
Once you have all three Netherstones, travel via the boat in the Undercity sewers to the Morphic Pool. Confront the Elder Brain. You will need to make several extremely difficult ability checks (DC 99). Even if you roll a Natural 20, the brain breaks free and evolves into a Netherbrain, forcing the Emperor to rescue you into the Astral Prism.
2. The Ultimate Choice (The Prism)
Inside the Prism, the Emperor reveals that only an Illithid mind can wield the Netherstones to dominate the brain. You must make the game's biggest decision:
- Side with The Emperor: Give him the stones. He consumes Orpheus' brain, granting him the power. Lae'zel will be furious (potentially turning hostile unless persuaded).
- Free Orpheus: Refuse the Emperor. Feeling betrayed, he leaves to join the Netherbrain! You must then use the Orphic Hammer to free Prince Orpheus.
- The Mind Flayer Sacrifice: If you free Orpheus, someone MUST turn into a Mind Flayer to wield the stones. Orpheus will volunteer to do it, Karlach will volunteer (saving her from her engine blowing up), or your main character can do it.
3. High Hall Courtyard
You leave the prism into the ruins of the High Hall. Give your rousing speech to your gathered allies. During the ensuing combat sections, you gain a new action: Call Forth Allies. This lets you summon squads of NPCs you've helped (like the Owlbear, Harpers, Gur, or Hellriders) to fight for you.
Push through the courtyard, taking cover from the nautiloid artillery strikes. It is highly recommended to cast Invisibility on your party and simply run/fly past the gauntlet of enemies straight to the brain stem.
4. Atop the Netherbrain
Climb the brain stem. You find yourself on top of the brain's cortex. A massive Red Dragon, Emperor (if betrayed), Dream Guardians, and Mind Flayers await.
You have a turn limit before a Nautiloid arrives to bombard you. Do not try to kill every enemy here. Cast Globe of Invulnerability in front of the Crown of Karsus. Move your Mind Flayer character inside the globe and channel the spell "Karsus' Compulsion" on the crown. Once the channel completes (takes 1 turn), a portal into the brain's psyche opens. Rush your entire party inside!
5. The Grand Finale
Inside the psyche, you fight the physical manifestation of the Netherbrain. It takes increased damage from everything. Unleash your absolute strongest attacks, Action Surges, and highest-level spells.
Important Mechanic: At the end of every turn, the Brain marks the platforms where your characters are standing. On the following turn, those platforms will disintegrate, instantly killing anyone still standing on them. KEEP MOVING!
Once its HP reaches 0, the final cutscene plays. You have one last choice: command the brain to destroy all tadpoles and itself (Good Ending), or betray your allies, claim the absolute power for yourself, and conquer the world "in Bhaal's name" or your own (Evil Ending).
6. Withers' Party (Epilogue)
✅ Six Months Later...
If you chose the Good Ending, Withers hosts a reunion party at the campsite 6 months after the battle. You can walk around, read letters in your chest from NPCs you helped across all three acts, talk to your romanced partner, and catch up with every companion to see where their lives went.
Speak to Withers when you are ready to conclude the game. Congratulations on completing one of the greatest RPGs ever made!
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