The Netherbrain/Combat

The Unbreakable Will of the Netherbrain
Huge Aberration
Level 20 Elder Brain
Stats
Armour Class	15
Hit points	300 (Balanced) 450 (Tactician)
Movement speed	0 m (0 ft)
Weight	10000 kg (20000 lb)
Initiative	-15
Ability scores
STR DEX CON INT WIS CHA 14 (+2) 10 (0) 22 (+6) 28 (+9) 21 (+5) 24 (+7)
Proficiency bonus	+4
Saving throws	Str +2 Dex 0 Con +10 Int +13 Wis +9 Cha +11
Conditions
Chains of Karsus	Will break free of its domination within 5 turns
Against All Odds	Begins with a portion of its HP missing, depending on an earlier ability check
Features
Psionic Retribution	Use a reaction to release a brainquake
Actions
Retributive Brainquake	10d6Psychic and  Mindbroken in response to damage.
Orb of Negation	Mark platforms for negation, destroying them the next turn.

Overview

Combat

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

Spells and abilities

 Retributive Brainquake ()

10d6 (10~60) Psychic

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 / 90 ft

 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 /  ft

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 to dominate the Netherbrain at the Morphic Pool it will have this condition, which will greatly reduce its HP.

Enemy allies

• Dominated Red Dragon
• Illithid Arcanist x4
• Tentacle x16 (hidden under the brain's surface until approached)
• Nautiloid (Creature) (appears after a 4 turn countdown and begins summoning Mind Flayers and Intellect Devourers)

Conditional enemy allies

• The Emperor (if the player chose to side with Orpheus)
• Dream Guardian x4 (if the player chose to side with Orpheus)
• Countermeasure x4 (if the player chose to side with the Emperor)

Encounter

Atop the brain

• Dimension Door, Arcane Gate and Misty Step are all useful spells to have assigned or distributed as scrolls for moving from the entrance Atop the Netherbrain to the Crown of Karsus.
• Stepping directly on the brain's surface will summon hidden tentacles, so it may be easier to approach from the two platforms on either side. Otherwise, if intending to sprint across, it is helpful to use a character who can avoid Opportunity Attacks, such as one with the Mobile feat.
• Globe of Invulnerability is also useful for protecting the caster of Karsus' Compulsion. However, the nearby Mind Flayers will still be able to  stun creatures inside the globe, which ends the spell prematurely.
  • Tossing Mind Flayers over the edge with moves like Telekinesis will not kill them, as they will just reappear atop the Netherbrain.
• Only party members and Orpheus or the Emperor can enter the Netherbrain's psyche (or The Unbreakable Will of the Netherbrain), so once the portal is open it is no longer necessary to continue fighting other enemies.

Inside the crown

• On Tactician, the Netherbrain will have 450 hit points.
• The Netherbrain's hit point total can be reduced by 20% for the final fight via  Against All Odds if the player rolled a natural 20 for the final skill check to dominate the Netherbrain in the Morphic Pool.
• The first attack each round against the Brain will cause it to use Retributive Brainquake, which will damage and potentially  Slow everything in range.
• The Brain will use Orb of Negation to summon several orbs which cause damage at the end of the next round. These orbs will destroy the platforms beneath them, so it is important to move characters off of any marked platforms. Further, the brain should be quickly killed since every platform will be destroyed in only a couple of turns.
• It is strongly recommended to have one's entire party near the portal before casting Karsus' Compulsion. Once the final fight against the Netherbain begins, it is possible for the Netherbrain to negate all platforms near the portal, preventing party members caught outside from entering.

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.