Neothelid — Colossal Psychic Worm of the Deep
A gargantuan psychic worm whose acid breath, crushing mind powers and immense appetite make it a nightmare even to other aberrations.
The neothelid is a colossal, tentacled worm with a lamprey-like maw, immense strength and a mind powerful enough to kill at range. In the illithid tradition, a neothelid is what happens when tadpoles survive without being implanted into hosts: one consumes the others, grows far beyond the form intended for it and becomes a creature that Mind Flayers regard as a biological catastrophe. Pathfinder presents a related but distinct subterranean psychic horror with ancient cults, acid breath and powerful mental attacks.
At a Glance
Run It Tonight
A neothelid should arrive as a disaster. Let the party discover an abandoned psychic colony, a tunnel bored straight through worked stone, or a trail of half-digested aberrations before the monster appears. In battle, it opens with acid or psychic force, then uses its bulk and reach to break the formation and swallow whoever becomes isolated.
Rules by Edition
Neothelid
Gargantuan Aberration, typically Chaotic Evil
AC 17; Initiative −2 (8)
HP 310 (20d20 + 100)
Speed 30 ft., Burrow 30 ft.
25 (+7)
7 (−2)
21 (+5)
4 (−3)
16 (+3)
15 (+2)
Saving Throws Con +10, Wis +8
Skills Perception +8
Resistances Acid, Psychic
Immunities Charmed, Frightened
Senses Blindsight 120 ft.; Passive Perception 18
Languages understands Deep Speech; telepathy 120 ft.
CR 13 (10,000 XP); PB +5
Traits
Magic Resistance. The neothelid has Advantage on saving throws against spells and other magical effects.
Trace Teleport. When a creature teleports from or to a space within 60 feet of the neothelid, the neothelid learns the direction and approximate distance to the other end of that teleport for 1 minute.
Actions
Multiattack. The neothelid makes one Bite and two Tentacle attacks.
Bite. Melee Attack Roll: +12, reach 10 ft. Hit: 29 (4d10 + 7) Piercing damage. A Huge or smaller creature hit by the Bite can be Grappled (escape DC 19).
Tentacle. Melee Attack Roll: +12, reach 20 ft. Hit: 18 (2d10 + 7) Bludgeoning damage plus 9 (2d8) Psychic damage.
Acid Breath (Recharge 5–6). Each creature in a 60-foot Cone makes a DC 18 Dexterity saving throw, taking 63 (14d8) Acid damage on a failure or half as much on a success.
Mind Thrust (Recharge 5–6). One creature the neothelid can sense within 120 feet makes a DC 18 Intelligence saving throw, taking 44 (8d10) Psychic damage on a failure or half as much on a success.
Psychic Crush (1/Day). One creature within 60 feet makes a DC 18 Wisdom saving throw. On a failure, it takes 55 (10d10) Psychic damage and has the Stunned condition until the end of its next turn. On a success, it takes half damage only.
Swallow. The neothelid swallows one Huge or smaller creature it is Grappling with its Bite. A swallowed creature has Total Cover against effects outside the neothelid and takes 21 (6d6) Acid damage at the start of each of the neothelid’s turns. If the neothelid takes 35 damage or more on a single turn from a creature inside it, it must succeed on a DC 18 Constitution saving throw or regurgitate all swallowed creatures.
Neothelid
Gargantuan aberration, chaotic evil
Armor Class 17 (natural armor)
Hit Points 310 (20d20 + 100)
Speed 30 ft., burrow 30 ft.
25 (+7)
7 (−2)
21 (+5)
4 (−3)
16 (+3)
15 (+2)
Saving Throws Con +10, Wis +8
Skills Perception +8
Damage Resistances acid, psychic
Condition Immunities charmed, frightened
Senses blindsight 120 ft., passive Perception 18
Languages understands Deep Speech, telepathy 120 ft.
Challenge 13 (10,000 XP)
Traits
Magic Resistance. The neothelid has advantage on saving throws against spells and other magical effects.
Trace Teleport. The neothelid senses the destination or origin of a teleport used within 60 feet for 1 minute.
Actions
Multiattack. The neothelid makes one bite and two tentacle attacks.
Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 29 (4d10 + 7) piercing damage, and a Huge or smaller target can be grappled (escape DC 19).
Tentacle. Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 18 (2d10 + 7) bludgeoning damage plus 9 (2d8) psychic damage.
Acid Breath (Recharge 5–6). Each creature in a 60-foot cone must make a DC 18 Dexterity saving throw, taking 63 (14d8) acid damage on a failed save or half as much on a success.
Mind Thrust (Recharge 5–6). One creature within 120 feet must make a DC 18 Intelligence saving throw, taking 44 (8d10) psychic damage on a failure or half as much on a success.
Swallow. The neothelid swallows one Huge or smaller creature grappled by its bite. The creature takes 21 (6d6) acid damage at the start of each of the neothelid’s turns until it escapes.
Neothelid CR 15
XP 51,200
CE Gargantuan aberration
Init +2; Senses blindsight 100 ft., trace teleport 60 ft.; Perception +25
Defense
AC 30, touch 4, flat-footed 30 (−2 Dex, +26 natural, −4 size)
hp 230 (20d8+140)
Fort +15, Ref +4, Will +16
DR 10/cold iron; SR 26
Offense
Speed 30 ft., fly 60 ft. (good)
Melee 4 tongues +21 (3d6+10/19–20 plus grab)
Space 20 ft.; Reach 20 ft.
Special Attacks breath weapon (50-ft. cone, 14d10 acid, Reflex DC 27 half, every 1d4 rounds), mind thrust, psychic crush, swallow whole (2d6+10 plus 2d6 acid, AC 23, hp 23)
Spell-Like Abilities CL 20th
Constant—fly
At will—detect thoughts, charm monster, clairaudience/clairvoyance, suggestion, telekinesis, teleport, poison
3/day—quickened suggestion
Statistics
Str 30, Dex 7, Con 24, Int 16, Wis 15, Cha 21
Base Atk +15; CMB +29 (+33 grapple); CMD 37 (can’t be tripped)
Feats Cleave, Great Cleave, Great Fortitude, Improved Bull Rush, Improved Critical (tongue), Improved Initiative, Improved Overrun, Iron Will, Power Attack, Quicken Spell-Like Ability (suggestion)
Skills Bluff +25, Climb +33, Diplomacy +25, Intimidate +28, Knowledge (arcana) +26, Perception +25, Spellcraft +26
Languages Aklo, Terran, Undercommon; telepathy 100 ft.
Special Abilities
Mind Thrust (Su). Three times per day, one target within 60 feet takes 15d10 damage unless it succeeds on a DC 25 Will save, which negates the effect. This is mind-affecting.
Psychic Crush (Su). Three times per day, one target within 60 feet must succeed on a DC 25 Will save or collapse unconscious and dying. On a success, it instead takes 6d6 damage and is sickened for 1 round.
Trace Teleport (Ex). The neothelid learns the mental coordinates of the destination of a teleport effect used within 60 feet. The knowledge lasts 1 minute.
Ecology
Environment any underground
Organization solitary, pair or cult (3–5 plus charmed slaves)
Treasure standard
Neothelid
Gargantuan Aberration
Hit Dice 20d8+140 (230 hp)
Initiative +2
Speed 30 ft., fly 60 ft. (good)
Armor Class 30 (−4 size, −2 Dex, +26 natural), touch 4, flat-footed 30
Base Attack/Grapple +15/+37
Attack tongue +21 melee (3d6+10/19–20)
Full Attack 4 tongues +21 melee (3d6+10/19–20 plus improved grab)
Space/Reach 20 ft./20 ft.
Special Attacks acid breath, mind thrust, psychic crush, swallow whole, spell-like abilities
Special Qualities blindsight 100 ft., DR 10/cold iron, SR 26, trace teleport 60 ft.
Saves Fort +15, Ref +4, Will +16
Abilities Str 30, Dex 7, Con 24, Int 16, Wis 15, Cha 21
Skills Bluff +25, Climb +33, Concentration +30, Intimidate +28, Knowledge (arcana) +26, Listen +25, Spellcraft +26, Spot +25
Feats Cleave, Great Cleave, Great Fortitude, Improved Bull Rush, Improved Critical (tongue), Improved Initiative, Improved Overrun, Iron Will, Power Attack, Quicken Spell-Like Ability (suggestion)
Environment underground
Organization solitary or cult
Challenge Rating 15
Treasure standard
Alignment usually chaotic evil
Mind Thrust (Su)
Three times per day, the neothelid can target one creature within 60 feet. Will DC 25 negates; on a failed save the target takes 15d10 damage. Mind-affecting.
Psychic Crush (Su)
Three times per day, one creature within 60 feet must make a DC 25 Will save. Failure leaves it unconscious and dying; success deals 6d6 damage and sickens it for 1 round.
Trace Teleport (Ex)
The neothelid learns the destination of a teleport effect used within 60 feet for 1 minute.
Origins: Two Traditions
Illithid tradition. A neothelid forms when illithid tadpoles remain in a brine pool without being implanted into hosts. Cannibalism leaves one survivor that continues growing into an immense worm. Mind Flayers regard the result as obscene, dangerous and evidence of a catastrophic failure of their reproductive order.
Pathfinder tradition. The PF1e creature is a distinct ancient subterranean psychic horror: an intelligent, spell-using worm served by lesser creatures and associated with powers beyond the known world. The PF tab preserves that separate presentation rather than forcing the illithid origin onto it.
Behaviour
A D&D-style neothelid is hunger given psychic power. It is intelligent enough to stalk prey and recognise danger, but it lacks the discipline and culture of an elder brain or mature illithid colony. It devours anything useful and reacts violently to creatures associated with Mind Flayers.
The Pathfinder version is more calculating. It can maintain charmed servants, use teleportation and mental effects deliberately, and establish a cult-like territory around itself.
Signs Before Initiative
- A tunnel has been widened by something enormous forcing its body through worked stone.
- Mind Flayer remains show signs of having been eaten rather than ritually preserved.
- Brine pools are empty except for torn membranes and deep gouges in the walls.
- Victims are physically intact but show catastrophic psychic trauma.
- Teleporting scouts report an immediate sensation that something noticed where they went.
- Acid-scarred stone marks a cone-shaped kill zone across a cavern floor.
If Violence Starts
The neothelid opens at range with acid or psychic force. Once the party spreads out, it uses its reach and bulk to seize a vulnerable target and swallow it. Do not run it as a stationary sack of hit points: burrowing, flight in the PF tradition and psychic control should keep the battlefield changing.
Counterplay
Spread out before the acid breath lands, protect low-Intelligence or low-Wisdom characters from psychic effects, and have a plan for a swallowed ally. Teleportation is not automatically safe against the older neothelid because Trace Teleport can reveal where a fleeing creature went.
If the campaign uses the illithid origin, knowledge of Mind Flayer biology can reveal where the creature is likely to lair: abandoned colonies, forgotten brine pools and tunnels once used for ceremorphosis.
Using a Neothelid in an Encounter
The empty colony. Every Mind Flayer in a hidden enclave is dead. The brine pool is empty and one tunnel has been widened from the inside.
The thing that followed. The party teleports away from a deep ruin, then discovers the monster knows exactly where they escaped to.
The acid road. A subterranean trade route has become unusable because entire caravan formations are being erased in cone-shaped acid attacks.
The forbidden offspring. A surviving illithid offers information and safe passage if the party destroys a neothelid before the rest of its colony learns the creature exists.
Related Creatures
Compare the neothelid with the Mind Flayer, the Roper and other deep-earth aberrations in the Aberration Bestiary. Return to the World Bestiary for the wider monster index.
Rules Sources and Licensing
The Pathfinder 1e block preserves the open rules material formerly used on this page. The D&D 3.5e block is a compatibility presentation of the legacy high-level psychic worm. The 5e/2014 and 5.5e/2024 blocks are original compatibility adaptations and are not represented as official SRD statistics.
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