Reducing the Netherbrain's Dexterity to 0 instantly kills it and skips the surrender sequence
Halotydeus
6 hours ago
A character must have the Illithid passive Ability Drain.
At the beginning of the encounter (5 turns remaining), cast Synaptic Consumption on the Netherbrain (DEX 10 → 5). Synaptic Consumption then reduces the Netherbrain's Dexterity by 1 at the end of each round, just after the Netherbrain finished its turn. However, Synaptic Consumption alone is not enough. On the final turn, the Chains of Karsus break before the fifth Dexterity reduction can occur, leaving the Netherbrain at DEX 1 instead of 0.
To overcome this, hit the Netherbrain once with a bow (or any DEX-based attack) during the fight while having the Ability Drain passive. This applies Ability Drain Dexterity, reducing DEX by 1.
With Ability Drain Dexterity, the sequence is:
Round 1 (5 Turns Remaining)
Players act
Synaptic Consumption: DEX 10 → 5
Ability Drain (DEX): 5 → 4
Netherbrain acts
End of Netherbrain's turn: 4 → 3
Round 2 (4 Turns Remaining)
Players act
Netherbrain acts
End of Netherbrain's turn: 3 → 2
Round 3 (3 Turns Remaining)
Players act
Netherbrain acts
End of Netherbrain's turn: 2 → 1
Round 4 (2 Turns Remaining)
Players act
Netherbrain acts
End of Netherbrain's turn: 1 → 0
→ Instant death
Synaptic Consumption had to be applied on the first round, when 5 turns remained.
Ability Drain: Dexterity only needs to be applied once. It does not necessarily have to be applied on the first round; it only needs to happen before the final Synaptic Consumption tick.
Without Ability Drain: Dexterity, the sequence is:
Round 1
DEX 10 → 5
End of Netherbrain's turn
DEX 5 → 4
Round 2
DEX 4 → 3
Round 3
DEX 3 → 2
Round 4
DEX 2 → 1
Round 5 (1 Turn Remaining)
Players act
Netherbrain acts
Chains of Karsus breaks
Combat ends
The final Synaptic Consumption tick never resolves.
During my testing, I also confirmed several important mechanics:
1. Synaptic Consumption and Absorb Intellect share the same mutually exclusive status and cannot both be applied to the same target.
2. Ability Drain can coexist with Synaptic Consumption.
3. Different Ability Drain effects (e.g. Strength and Dexterity) can coexist on the same target.
4. The Netherbrain is not immune to ability scores being reduced to 0.
5. The casters do not need to survive. I tested this by letting both the Illithid (casting Synaptic Consumption) and the character applying Ability Drain: Dexterity die immediately after applying their effects.
The remaining companions stayed outside the Netherbrain arena, yet the Netherbrain still died automatically when its Dexterity reached 0.
6. Death caused by reducing an ability score to 0 bypasses the Netherbrain's normal death sequence. Netherbrain died immediately and could not surrender. In one of my tests, the game skipped directly to Withers' epilogue party. In another test using the same method, the normal ending cutscene played, but the Netherbrain still died instantly without entering Netherbrain's surrender sequence.
