Everything that happens in Baldur's Gate 3 leads up to one final moment: a confrontation with the Netherbrain. This Elder Brain, also called the Absolute, has evolved thanks to long contact with the Crown of Karsus and become far more dangerous than any other Elder Brain in the illithid empire.
As the final boss of Baldur's Gate 3, this fight is a tough one even for a level 12 party covered in endgame gear. The second phase of the fight is especially brutal thanks to the way the Netherbrain fights. Fortunately, a little preparation can go a long way towards making this fight much easier for any party composition.
Phase One
After enduring a two-stage fight against Absolutist forces, players can use a full-restore object and then climb up the Netherbrain's spinal cord. The Netherbrain will lift into the air, but not before the party climbs aboard. Once the party reaches the top, phase one of the final battle will begin. Enemy forces include:
- A psychically dominated adult red dragon
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Four illithid arcanists who love casting high-level Magic Missile and start with
Fire Shield
active
- A series of tentacles that reveal themselves when a party member or ally gets too close, and that try to grapple anyone nearby
- After four rounds, a nautiloid will approach. Much like the nautiloid fight earlier, it can bombard sections of the battlefield with Fire and Force damage and summon reinforcements.
- If players rejected the Emperor in the Astral Prism, he'll arrive on top of the red dragon and create one Dream Guardian for each party member.
The goal of this fight is to get the party illithid (whoever it is) to the Crown of Karsus on the opposite end of the brain. The party illithid must then spend their action to influence the Netherbrain. If they get hit with Incapacitated, Stunned, Polymorphed, or Knocked Out, they must start again. If they don't, a portal to the Netherbrain's psyche will open and phase two will begin. Bear in mind that Karsus' Compulsion has a 20-foot range, so the caster must get close.
With so many moving parts, players can feel overwhelmed. However, a good strategy can help the party pull through and reach the second phase.
- Players can afford to ignore the Dream Guardians. They mostly spend their turns teleporting around and casting a variation of Command to try and stop or silence their assigned party member, and the save DC for this ability is fairly low.
- On the other hand, don't ignore the Emperor. If possible, focus on him first and try to take him down in one round.
- The red dragon is also dangerous, but it has 400 hit points. It does a lot of damage and can hit groups of people with its flame breath and multiattack, but on the bright side it's too big to fit on the metal walkways along the edge of the battlefield. Hold Monster can stop it in its tracks, and allies summoned by spells or Call Forth Allies can keep it busy.
- If players take the time to kill the red dragon, they'll get the achievement Interfectorem Draconis.
- The tentacles can appear anywhere on the brain, but they can't appear on the metal walkways. Players should send some party members onto the walkways to get up and around to the Crown of Karsus.
- The illithid arcanists target whoever is closest to their position, making them another good reason to summon in reinforcements.
- The tentacles can stop a character in mid-jump by appearing, but they can't stop someone who's teleporting, levitating, or flying.
- The most important tip is this: gather the party by the Crown of Karsus before using Karsus' Compulsion. Doing so will make phase two much, much easier.
Phase Two
Karsus' Compulsion opens a portal to the Netherbrain's Psyche. Characters appear on a random platform around 60 to 70 feet away from the Unbreakable Will of the Netherbrain, and the goal of this phase is to deal 200 damage to the UWN in under five rounds. If the party fails to do so, the Netherbrain will transform them into mind flayers and the game will end.
The UWN can't move, but it has two ways to hurt the party. First, it has a reaction called Psionic Retribution that can hit the attacker and any nearby party member with Psychic damage and the Mindbroken condition. Fortunately, the UWN only has one reaction per round.
Second, the UWN can create Orbs of Negation on its turn. These orbs take one turn to activate and also deal Psychic damage, but more importantly they also destroy every nearby platform. If a party member is on one of these platforms when it disappears, they die instantly. Fortunately, the affected platforms glow red, making them easy to spot. Just make sure to move any Mindbroken characters to safety before trying to have them attack.
Because the UWN destroys platforms every round, this fight gets harder the longer it goes on. That's why players should bring every party member close to the Crown of Karsus before opening the portal. If the party can hit the UWN with everything they have during the first round of phase two, it'll go down before it can create even one Orb of Negation.
Another factor in this fight is how well players did during the first attempt to dominate the Netherbrain. While even a natural 20 against the DC 99 check won't win the game instantly, it'll apply a special condition called Against the Odds that causes the UWN to start with fewer hit points.
Once the Unbreakable Will of the Netherbrain falls, the party illithid will attempt to either destroy or dominate the Netherbrain. If the illithid isn't the protagonist, players can betray them to choose the other option. Either way, all that's left of the game is to have a chat with the party about what happens next.
Baldur's Gate 3 is available now on macOS, PC, and PS5.