I recast these guys more as muscle in my version of Valley of the Brain Collectors as since its a home game I could throw in mind flayers. These guys scared the heck out of my party. Even mind flayer thugs are smart. In terms of how many brains they had I just rolled 1d10 before the battle started.
The initial encounter with the party was between the three Shipmind watchers on the dropship. They focussed their mental attacks against the lowest wisdom character in the party – Brockthor the Fighter – he was hit twice with mind worms and once with whispers of madness – each boosted with cerebral power and he managed to make all the rolls using every re-roll/bonus he had – inspiration, fate points, lucky and Indomitable. He was mentally exhausted after it. After this battle I added celerity to the list of abilities allowing higher brain count versions to both do a psionic attack and melee if they so chose. Making them very deadly CR 8 monsters. For the advanced neh-thalgaa later in the adventure I just gave it a full 10 brain compliment which seemed to work well.
Large aberration, chaotic evil
Armour Class 16 (natural armour)
Hit Points 127 (15d10 +45)
Speed 10 ft., fly 40 ft.
Initiative Speed +2 (Dex +2)
STR 20 (+5) DEX 15 (+2) CON 16 (+3)
INT 19 (+4) WIS 17 (+3) CHA 17 (+3)
Saving Throws Int +7, Wis +6, Cha +6
Skills Arcana +7, Insight +6, Perception +6, Stealth +5
Damage Resistance bludgeoning, piercing, and slashing from nonmagical weapons
Condition Immunities charmed, frightened Senses darkvision 60 ft., passive Perception 16
Languages: Common, Abyssal, Aklo, Draconic, Protean, Uncommon, telepathy 100 ft.,
Challenge 8 (3,900 XP)
Brain Collection. The brain collector can store up to ten humanoid brains and use them to enhance its knowledge and power. The destruction of these brains causes the brain collector to lose some of its magical power. Each brain can be attacked (AC 20: 15 hit points). Destroying a single brain deals no damage to the brain collector, but causes it to lose special abilities. The number of brains determines its additional special attacks. It may use these abilities once per day. It may also maintain as many concentration spells as it has brains:
- 0: No additional special abilities.
- 1-4: Mind Worm. +7 ranged magical attack, the target takes must make a DC 16 Wisdom save or have disadvantage on Wisdom saving throw’s until the neh-thalgaa is dead or lost all its brains. The target is also slowed as the spell.
- 5: Whispers of Madness. +7 ranged magical attack; on a hit the target takes 16 (3d8 +4) psychic damage and must pass a DC 16 Wisdom save or become slowed. If already slowed the target is parlayed
- 6: Celerity. The neh-thalgaa may make its normal attacks and as bonus may use a psionic ability or attack listed on this table.
- 7: Invisibility. As the spell of the same name.
- 8: Bend Space. The neh-thalgaa gains a reaction. If the neh-thalgaa would be hit by an attack it can teleport up to 15 feet. This does not provoke an attack of opportunity.
- 9: Distortion Blast. All creatures in a 100-foot long line that is 5 feet wide must make a DC 16 Wisdom save or take 28 (8d6 +4) psychic damage. Aberrations have advantage on this save and only take half damage.
- 10: Venomous Mind. All creatures within melee range of the neh-thalgaa must make a DC 16 Wisdom save or take 8 (1d8 +4) psychic damage and become disorientated. The creature then uses its reaction to make a single melee attack against a random adjacent enemy.
Cerebral Power (Recharge 6). The brain collector uses the power of its collected brains to supercharge its magic. The brain collector can use this ability as a bonus action to cause the target of one of its spells to make any saving throws against the spell at disadvantage.
Magic Resistance. The brain collector has advantage on saving throws against spells and other magical effects.
Strange Knowledge. A neh-thalgaa may add its proficiency bonus to all knowledge related skill checks.
Multiattack. The brain collector makes three attacks: one with its bite and two with its claws. Additionally it can make a Collect Brain attack if it is able.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target.
Hit: 9 (1d8 + 5) piercing damage, and the target must succeed on a DC 15 Constitution saving throw or be poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target.
Hit: 12 (2d6 + 5) slashing damage. If the target is an creature, it is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the neh-thalgaa can’t use one of its claw attacks on another target. However the grappled creature automatically takes 14 (2d6 + 7) bludgeoning damage at the start of the neh-thalgaa’s turn.
Collect Brain. Melee Weapon Attack: +8 to hit, reach 5 ft., one incapacitated humanoid grappled by the brain collector.
Hit: The target takes 55 (10d10) slashing damage. If this damage reduces the target to 0 hit points, the brain collector kills the target by extracting and collecting its brain.
This crab-like nightmare has a lamprey mouth, twitching eyes on its legs, and several blisters along its back that hold human brains.