The Netherbrain/Combat

Overview

Combat

This page focuses on The Netherbrain's behavior during turn-based combat gameplay.

Attacks and abilities

 Orb of Negation ()

The Grand Design cannot be disrupted - manifest an orb of Netherese arcana that explodes on its turn, obliterating everything within range.

 Range: 30 m / 100 ft

 Retributive Brainquake ()

Damage: 10~60

10d6Psychic

Upon first time that you take damage in a turn, emit a wave of psionic force that  Mindbreaks nearby enemies.

INT Save

 Range: 30 m / 100 ft

AoE: 12 m / 40 ft (Radius)

Honour Mode

 Aegis of the Absolute

The Netherbrain can make itself Immune to all types of damage it took in a round of combat until the start of its next turn.

 Range: 18 m / 60 ft

Recharge: Per turn

Conditions

•  Chains of Karsus - After using Karsus' Compulsion on the Netherbrain.
•  Against All Odds - If a natural 20 was rolled on the final check (DC 99) to dominate the Netherbrain at the Morphic Pool it has this condition, which reduces its HP by 20%.

Allies

• Dominated Red Dragon
• Illithid Arcanist - 4x
• Nautiloid (Creature) (appears after a 4 turn countdown and begins summoning Mind Flayers and Intellect Devourers)
• Tentacle - 4x (hidden under the brain's surface until approached)

Conditional Allies

• Dream Guardian - 4x (if Orpheus was freed)
• Countermeasure - 4x (if the Emperor was sided with)
• The Emperor (if Orpheus was freed)

Encounter details

Atop the brain

The objective of the first phase is to make it to the Crown of Karsus and channel  Karsus' Compulsion on it to enter the Netherbrain's psyche and defeat it for good. Stepping directly on the brain's surface summons up to 16 hidden tentacles, so it may be easier to approach from the two platforms on either side.

Once reaching the Crown of Karsus, the party member with  Karsus' Compulsion must channel it in order to enter the final stage of the fight. The channeling takes both action and bonus action to initiate, and must last until the next turn of the caster to succeed. If succeeded upon the caster's next turn, a portal opens to the Netherbrain's psyche (or The Unbreakable Will of the Netherbrain).

Only party members and either Orpheus or the Emperor can enter this portal, so once it has been opened there is no reason to continue fighting other enemies.

Once all party members and Orpheus / the Emperor have entered the portal, the battle outside on the surface of the brain ends and the remaining turn order only consists of the party and the Netherbrain.

Inside the crown

• It is strongly recommended to have the entire party near the portal before completing Karsus' Compulsion. Once the portal is opened, the final fight against the Netherbrain begins immediately and it must be defeated before it destroys all the platforms inside.
• While allies summoned through  Gather Your Allies cannot enter the portal, they can be summoned onto the platforms inside.
• The Netherbrain uses  Orb of Negation to summon several orbs which deal damage at the end of the next round and destroy the platforms beneath them, so it is important to move characters off of any marked platforms. These Orbs disappears upon the brain's death.
• The Netherbrain must be killed quickly since every platform can be destroyed in only a couple of turns.

Tactics

Atop the brain

•  Dimension Door,  Arcane Gate, and  Misty Step are all useful spells / scrolls for moving from the entrance Atop the Netherbrain to the Crown of Karsus. Otherwise, if intending to sprint past the tentacles hidden under the brain's surface, it is helpful to use a character who can avoid Opportunity Attacks, such as one with the Mobile feat.
•  Fly (Illithid Power) is incredibly strong in this fight. Both sections of the fight reward high mobility, since you need it to reach the crown and escape exploding platforms. A character with this ability can also quickly reach the Illithid Arcanists and kill them before they begin bombarding the party with their extra long range  Magic Missile.
•  Globe of Invulnerability and  Sanctuary are useful for protecting the caster of  Karsus' Compulsion. However, the nearby Illithid Arcanists can still  stun creatures affected by these spells, which disrupts the spell prematurely.
• The four Illithid Arcanists are very dangerous enemies in this section of the fight. They can spam a more powerful version of  Magic Missile, use  Counterspell, stun the party members via  Tentacle Whip and  Mind Blast, and even gain control of allies with  Mind Flayer Domination. They are also immune to being pushed over the edge with moves like Telekinesis, as they just reappear atop the Netherbrain. Fortunately they have a rather low number of hit points, making them vulnerable to allies with high maneuverability and damage.
• The Countermeasures summoned while siding with the Emperor are far more dangerous than the Dream Guardians summoned while siding with Orpheus. Some of them have powerful disruptive abilities such as  Counterspell,  Psionic Dominance,  Goading Attack (Melee),  Slow,  Black Hole, and  Confusion which can severely hinder an unprepared party. Others have significantly more hit points (see Rage Queller) or deal far more damage through  Improved Extra Attack and  Action Surge (See Breaker of War).

Inside the crown

• Casting  Feather Fall before entering the portal can allow melee range party members with low movement speed to immediately jump down to the brain and begin attacking it.
• The first attack each round against the Brain causes it to use  Retributive Brainquake, which damages and possibly  slows everything in range. The party can potentially avoid this the first time by triggering it with the first party member to enter the portal, and then having the rest of the team enter afterwards.
•  Dimension Door and  Misty Step can help party members reach safe platforms if the ones they are on have been designated for destruction.
• On Honour Mode, the Netherbrain augments itself with  Aegis of the Absolute, making it immune to damage types that were used against it on the previous turn. It is important to plan ahead exactly which attacks are used against it to avoid missing entire turns where the brain is immune to all the party's attacks.

Achievements

Hero of the Forgotten Realms

Save the day: kill the Netherbrain and destroy the Absolute tadpoles.

Absolute Power Corrupts

Reign with terror: take control of the Netherbrain and bend the world to your will.

Sins of the Father

Claim your Throne of Blood: take control of the Netherbrain for Bhaal and break the world.

Bugs

• Thrown weapons that return to the user, such as Nyrulna or Returning Pike, may occasionally fall into the chasm below the Netherbrain and disappear forever after being thrown at it. Throwing builds should bring back-up weapons just in case. Targeting the brainstem of the Netherbrain (mostly) prevents returning weapons from falling into the chasm).