Made by a Mad Alhoon (Illithid based monsters)

[Zaydos]

Studying the illithids and their kind I came across references to a certain Marikus, a name which the illithids seemed loath to use. This Marikus was an ullitharid which had chosen to go down the path of wizardry and then took the forbidden step into undeath becoming an alhoon. While an ullitharid becoming an alhoon is reason enough for his name to be thought like a curse by illithids, Marikus did something far worse.

Marikus stole away with several years of larvae from the Elder Brain’s pool, preserving them for experimentation. This experimentation involved implanting illithid larvae into non-humanoid hosts. While many of the hosts rejected the larvae completely (usually in a manner fatal to both the larva and host), and others required special preparations to be performed on one or both first, several new illithid-kin were created this way. While the illithids destroyed Marikus for his research, they took his notes, and even now use some of his creations in the empire’s attempts to dominate.

In Lords of Madness they introduced urophions (these could predate LoM but it's my introduction to them at least) and they got me thinking that if non-humanoids could undergo cerebromorphosis and produce unique results why is it only ropers we get to see. So I made a few more, and have some on the mental back burner.

Ranthirid
Medium Aberration (Psionic)
Hit Dice: 6d8+6 (33 hp)
Initiative: +4
Speed: 40 ft (8 squares)
Armor Class: 18 (+4 Dex, +4 natural), FF 14, touch 14.
BAB/Grapple: +4/+5
Attack: Bite +8 melee (1d6+1 and trip)
Full Attack: Bite +8 melee (1d6+1 and trip)
Space/Reach: 5 ft/5 ft.
Special Attack: Extract, Psi-like Abilities, Trip
Special Qualities: Blink, Darkvision 60-ft, Dimension Door, Low-Light vision, Scent, Spell Resistance 10 (7 + CR), Telepathy 100-ft.
Saves: Fort +5, Ref +6, Will +6.
Abilities: Str 13, Dex 18, Con 13, Int 16, Wis 13, Cha 14
Skills: Hide +13, Listen +10, Sense Motive +10, Spot +10, Survival +10
Feats: Ability Focus (Mind Thrust), Great Fortitude, TrackB, Weapon Finesse
Environment: Underground
Organization: Solitary, pair, pack (2-8) or hunting party (2-8 and 1-2 illithids).
Challenge Rating: 3.
Treasure: Standard.
Alignment: Usually Lawful Evil
Advancement: 7-9 HD (Medium), 10-18 HD (Large).
Level Adjustment: –
A four legged creature approaches you, its hairless body has slimy blue-violet flesh. The creature is shaped somewhat like a bony dog, but its cranium is expanded backwards. Its canine snout has four cephalopodic tentacles which stretch out. The creature is indistinct, flickering between fully visible and invisible.

Rarely seen, one of Marikus’s successes was the creation of the ranthirids, or illithid-blink dogs. Created from the magical dogs the ranthirids retain their ability to blink through reality, but augment it with greater strength and speed as well as the ability to perform a variety of telepathic attacks.

Ranthirids are used by illithid enclaves as scouts and hunting hounds. Much like urophionsLoM, ranthirids live lives outside of the core of illithid society their loyalty rewarded with little more than the promise of joining the elder brain in death. Ranthirids are rarely created due to the difficulty of acquiring blink dog hosts, and when they are made it is to provide fast hitting and mobile tactical troops.

Ranthirids speak Undercommon but prefer to communicate through telekinesis.

Combat: Alone a ranthirid will use dimension door and telepathic powers to whittle away at a foe. Preferably they will be striking at night or in a tunnel system where their ability to teleport around walls or into the darkness allows them to retreat from the enemy after an attack and then return on foot to mind thrust and then retreat only closing once they can no longer release psychic blasts and even then preferring to charge a target and then teleport away.

In a pack a ranthirid will rush a group and use Mental Disruption. While the group is reeling from this effect the others will attack, hoping to take down or at least trip any unaffected targets. If a target seems particularly weak willed they may try to overwhelm it by a focused assault of mind thrusts, before turning to its allies. Against a single foe they may even release their Ego Whips instead of using Mental Disruption hoping to lock down the target that way.

Blink (Su): A ranthirid can use blink as the spell (caster level 8th), and can evoke or end the effect as a free action.

Dimension Door (Su): A ranthirid can teleport, as dimension door(caster level 8th), once per round as a free action. The ability affects only the ranthirid, which never appears within a solid object and can act immediately after teleporting.

Extract (Ex): A ranthirid can extract and devour the brain of a creature whose head is within reach of its mouth as a coup de grace. This kills most creatures instantly.

Psi-like Abilities: 1/day Ego Whip (Will DC 15); 3/day Mental Disruption (Will DC 15), Mind Thrust (4d10, Will DC 17). All ML 4.

Trip (Ex): A ranthirid that hits with a bite attack can attempt to trip its opponent using Dexterity instead of Strength (+8 check modifier) as a free action without making a touch attack or provoking an attack of opportunity. If the attempt fails, the opponent cannot react to trip the ranthirid.


Kallipsid
Large Aberration (Psionic)
Hit Dice: 8d8+32 (68 hp)
Initiative: +1
Speed: 20 ft (4 squares), burrow 20 ft
Armor Class: 18 (-1 size, +1 Dex, +8 natural), FF 17, touch 10.
BAB/Grapple: +6/+16
Attack: Bite +11 melee (2d8+6 and improved grab)
Full Attack: Bite +11 melee (2d8+6 and improved grab) and 2 claws +9 melee (2d4+3)
Space/Reach: 10 ft/10 ft.
Special Attack: Compelling Gaze, Extract, Improved Grab, Psi-like Abilities
Special Qualities: Darkvision 60-ft, Naturally Psionic, Spell Resistance 22 (14 + CR), Telepathy 100-ft, Tremorsense 60-ft.
Saves: Fort +8, Ref +3, Will +7.
Abilities: Str 23, Dex 13, Con 19, Int 12, Wis 13, Cha 16
Skills: Climb +11, Jump +10, Listen +12, Spot +8
Feats: Ability Focus (Compelling Gaze), Great Fortitude, Multiattack
Environment: Underground
Organization: Solitary or cluster (2-4)
Challenge Rating: 8.
Treasure: Standard.
Alignment: Always Lawful Evil
Advancement: by Character Class
Level Adjustment: –
The creature before you looks like some disgusting bug. Standing roughly 8-ft tall, it could almost be mistaken for an umber hulk. It is mostly distinguished by being thinner, with smaller arms, and the four tentacles that split off two from each of its massive mandibles. Its eyes are also different, lacking the compound eyes of an umber hulk instead merely having two pairs of eyes one massive like a deep sea squid’s and the other almost human.

A kallipsid is the result of an illithid tadpole implanted into an umber hulk. This results in a mentally inferior creature, but one whose physical power might make up for some of what they have lost intellectually. Kallipsids are becoming more popular in illithid city-states which have decided that thralls cannot be trusted with the protection of their illithid betters. Kallipsids eat less than a regular illithid, allowing them to serve as heavy infantry in battle, with their controlling gaze to pacify targets for extraction and their Id Insinuation power to sow dissent among enemy ranks. Kallipsids are also used for their burrowing abilities, like the umber hulks they are made from they are able to burrow through stone at a rate of 5 feet per round and only leave usable tunnels if they choose to. This, coupled with their strength to aid in construction, means illithids find kallipsids useful for more than just their combat ability.

Kallipsids serve poorly outside of battle, though. Despite their capabilities outside combat, kallipsids are generally surly and listless in such positions. Kallipsids love combat, seeking it out, and many illithids allow them to have their way and move out in raids against other underdark dwellers. Some illithid settlements have taken to hiring out kallipsids as mercenaries for their neighbors.

Kallipsids speak undercommon, but prefer to communicate with allies telepathically. Kallipsids prefer to communicate with enemies with their compelling gaze and claws, trying to talk to them typically just angers them further.

Combat: Kallipsids prefer to pop out of their tunnels in the midst of enemies, allowing their compelling gaze to render as many enemies as possible out of commission and then striking with their mandibles and claws at enemies that resist.

Compelling Gaze (Su): A kallipsid’s gaze has a range of 30-ft and creatures within it feel compelled to approach the kallipsid and offer themselves as its meal. A creature that fails its Will save (DC 19) against a kallipsid’s gaze drops anything they are holding and approaches the kallipsid offering their head to it and taking no other actions. They will not resist a kallipsid’s grapple attempts (allowing them to attach all 4 tentacles in 2 rounds with no need to roll), and lose any Dexterity bonus to AC although they are not helpless. A creature affected by this gaze is allowed a new save each round, but may take no actions in the round if they succeed at this time, and each time they are dealt damage. This is a mind-affecting compulsion effect. Illithids, and other related creatures (including any character with at least 3 illithid heritage feats), are immune to this ability.

Extract (Ex): A kallipsid that begins its turn with all four tentacles attached and that makes a successful grapple check automatically extracts the opponent’s brain, instantly killing that creature. This power is useless against constructs, elementals, oozes, plants, and undead. It is not instantly fatal to foes with multiple heads, such as ettins and hydras.

Improved Grab (Ex): To use this ability, a kallipsid must hit a Small, Medium, Large, or Huge creature with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and attaches a tentacle to the opponent’s head. A kallipsid can grab a Gargantuan or larger creature, but only if it can somehow reach the foe’s head. If a kallipsid begins its turn with at least one tentacle attached, it can try to attach its remaining tentacles with a single grapple check. The opponent can escape with a single successful grapple check or an Escape Artist check, but the kallipsid gets a +2 circumstance bonus for every tentacle that was attached at the beginning of the opponent’s turn.

Psi-like Abilities: At-will Id Insinuation (3 targets, Will DC 17) ML 8.


Meriphion
Medium Outsider (Evil, Lawful, Psionic)
Hit Dice: 12d8+36 (90 hp)
Initiative: +2
Speed: 40 ft (8 squares)
Armor Class: 21 (+2 Dex, +9 natural), FF 19, touch 12.
BAB/Grapple: +12/+16
Attack: Greatsword +19 melee (2d6+9) or Tentacle +19 melee (1d4+7 and improved grab); includes Metaphyical Weapon and Metaphysical Claw
Full Attack: Greatsword +19/+14/+9 (2d6+9) and 4 tentacles +14 melee (1d4+7 and improved grab); includes Metaphysical Weapon and Metaphysical Claw
Space/Reach: 5 ft/5 ft.
Special Attack: Extract, Improved Grab, Maneuvers (via feats), Mindblast, Psi-like Abilities
Special Qualities: Aura of Menace, Circle of Corruption, Damage Reduction 10/good, Darkvision 60-ft, Immunity to Electricity and Petrification, Martial Stance (via feat), Planar Step, +4 to saves vs Poison, Scent, Spell Resistance 28 (17+CR), Telepathy 100-ft, Tongues.
Saves: Fort +11, Ref +10, Will +14.
Abilities: Str 19, Dex 14, Con 17, Int 16, Wis 23, Cha 20
Skills: Bluff +20, Concentration +18, Diplomacy +24, Hide +17, Intimidate +22, Knowledge (any one) +18, Listen +21, Move Silently +17, Sense Motive +23, Spot +21, and Survival +21 (+25 when tracking via scent)
Feats: Ability Focus (Aura of Menace), Ability Focus (Mindblast), MindsightLoM, Martial Study (Burning Blade), Martial Stance (Holocaust Cloak), TrackB
Environment: Any land or underground
Organization: Solitary, pair, or cabal (3-6)
Challenge Rating: 11.
Treasure: Standard.
Alignment: Always Lawful Evil
Advancement: by Character Class
Level Adjustment: –
Standing over six feet tall, this muscular humanoid creature, has leathery, platinum colored skin. It’s head extends forward into an animalistic snout, but this snout actually splits apart into four tentacles and a cephelapodic beak. It holds a greatsword as it stands before you radiating a deep focus of intent, and a certain calm contempt; as if it views what stands before it as nothing but ants.

Possibly the real reason Marikus is so anathema to his kind, the meriphions are the result of specially prepared tadpoles being implanted into hound archons and successfully undergoing cerebromorphosis. Unlike ranthirids and kallipsids, though, meriphions are quite willful creatures unwilling to submit to illithid dominance but instead seeing themselves as the new master race. Extremely few in number, meriphions have been known to break into illithid settlements in attempts to steal tadpoles for their own procreation, and at least one report I’ve heard tells me of a fledgling city ruled by a meriphion in place of an elder brain.

Meriphions seek out positions of power over lesser beings, creating more “equals” through cerebromorphosis of other Hound Archons and, if my studies of Marikus’s notes are on the right path possibly through proper cerebromorphosis of Mt. Celestia petitioners. They are haughty and carelessly cruel by nature; lacking in true sadism but seeing no value in human emotion.

Meriphions speak Undercommon, Celestial and Common, as well as possessing a natural Tongues ability. They prefer reserving telepathic communication with their equals, or favorite pets.

Combat: A meriphion opens combat by moving in close to foes, preferably within range of its circle of corruption and with concealing amorpha active, and opening with either a mind blast or charm. Meriphions will then if they have not already done so mind blast opponents before attempting to kill the stunned individuals with their sword and tentacles often expending their martial talents at the beginning of the fight.

Aura of Menace (Su): An aura of power surrounds meriphions that fight or get angry. Any hostile creature within a 20-foot radius of a meriphion must succeed on a Will save DC 22 to resist its effects. The save DC is Charisma-based, and includes a +2 racial bonus. Those who fail take a –2 penalty on attacks, AC, and saves for 24 hours or until they successfully hit the meriphion that generated the aura. A creature that has resisted or broken the effect cannot be affected again by the same meriphion’s aura for 24 hours.

Circle of Corruption (Su): Non-meriphion creatures within 10-ft of a meriphion suffer a -1 penalty to AC and saving throws. This penalty increases by 2 (to -3) against charm and compulsion effects. A Magic Circle against [Alignment] that has its origin within a meriphion’s Circle of Corruption is suppressed and vice versa. A Protection from [Aligment] effect is suppressed within the area of a meriphion’s Circle of Corruption but protects the affected creature from the Circle of Corruption’s effects.

Extract (Ex): A meriphion that begins its turn with all four tentacles attached and that makes a successful grapple check automatically extracts the opponent’s brain, instantly killing that creature. This power is useless against constructs, elementals, oozes, plants, and undead. It is not instantly fatal to foes with multiple heads, such as ettins and hydras.

Improved Grab (Ex): To use this ability, a meriphion must hit a Small, Medium, or Large creature with its tentacle attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and attaches the tentacle to the opponent’s head. A mind flayer can grab a Huge or larger creature, but only if it can somehow reach the foe’s head. If a meriphion begins its turn with at least one tentacle attached, it can try to attach its remaining tentacles with a single grapple check. The opponent can escape with a single successful grapple check or an Escape Artist check, but the meriphion gets a +2 circumstance bonus for every tentacle that was attached at the beginning of the opponent’s turn.

Martial Maneuvers (Su): A meriphion’s feats give it a single maneuver usable 1/encounter. Wall of Blades allows the replacement of AC with an attack roll as an immediate action, while Burning Blade adds 1d6+6 fire damage to melee attacks for 1 round as a swift action.

Martial Stance (Su): A meriphion’s feats gives it a single martial stance Holocaust Cloak which causes any creature striking it in melee (unless with a reach weapon) to take 5 points of fire damage.

Mind Blast (Ps): This psionic attack is a cone 60 feet long. Anyone caught in this cone must succeed on a DC 22 Will save or be stunned for 3d4 rounds. The save DC is Charisma-based and includes Ability Focus. This ability is the equivalent of a 6th level power.

Planar Step (Sp): A meriphion may use Greater Teleport or Plane Shift as the spells at-will, but may only transfer themselves and up to 50 lbs of gear.

Psi-like Abilities: At-will Metaphysical Claw; 3/day Concealing Amorpha, Metaphysical Weapon, Psionic Charm, Psionic Lion’s Charge, Psionic Suggestion. ML 12.

Tongues (Su): A meriphon benefits from a continuous Tongues effect.

[WhiteLycan]

I have ALWAYS wanted to run an Illithid-based campaign. I think you should keep throwing monsters out there!

[Debihuman]

Good stuff here. :biggrin:

Debby

[Zaydos]

The big one is that an elder brain isn't supposed to be a battle against a giant floating brain shooting off chain lightning or energy waves. An Elder Brain is supposed to be primarily scary not for the power it holds in an upfront fight but because it is the great manipulator of an illithid city state able to orchestrate their actions, able to detect intruders and send minions to strike at them. In direct combat an elder brain is a horrifyingly powerful mind, but that is it. Properly prepared for an elder brain is far from an insurmountable challenge, and an elder brain should not be a challenge for epic level heroes, it should be a battle that can be fought while illithids still serve as usable foot soldiers. In my ideal elder brain encounter the Elder Brain itself is just an "ordinary encounter" (CR = party level), but is itself only a third or even a fourth of the encounter, a host of illithids (12ish) and some more melee brutes bringing up the rest of the encounter. Even then an elder brain is something of a puzzle boss, if properly prepared (Will save boosters, mind blank, [redundant] protection from evil) it is far from the largest threat, but an ill-prepared party is in great danger.

I'll return to making actually new creatures soon, but for now the 3.5 Elder Brain and even the Elder Brain of Thoon failed badly to capture what I feel an Elder Brain ought to be (an immobile tactician) and felt instead like flying doom brains, so I tried to make my own. Not sure about the CR.

Elder Brain
Huge Aberration (Psionic)
Hit Dice: 15d8+150 (217 hp)
Initiative: +7
Speed: 5 ft as a full round action, swim 5 ft as a full round action.
Armor Class: 13 (-2 size, -3 Dex, +4 natural, +4 deflection), FF 13, touch 9.
BAB/Grapple: +11/+19
Attack: -
Full Attack: -
Space/Reach: 10 ft/0 ft.
Special Attack: Mindblast, Psi-like Abilities
Special Qualities: Telepathy (2 miles), Blindsight 120-ft, Darkvision 60-ft, DR 15/magic, Spell Resistance 32 (17 + CR), Dual Existence, Bud Brain Golem, Cyclopean Mind, Psionic Deflection, Peer Through, Astral Distortion
Saves: Fort +15, Ref +3, Will +15.
Abilities: Str 10, Dex 5, Con 26, Int 25, Wis 22, Cha 23
Skills: Bluff +23, Concentration +26, Diplomacy +27, Knowledge (any 4) +37, Knowledge (any other) +19, Sense Motive +25, Spellcraft +25
Feats: Ability Focus (Mind Blast), Ability Focus (Psionic Dominate), Great Fortitude, Improved Toughness x2, MindsightLom, B
Environment: Any land or underground
Organization: Solitary, pair, or cabal (3-6)
Challenge Rating: 15.
Treasure: Double Standard.
Alignment: Always Lawful Evil
Advancement: by Character Class
Level Adjustment: –
Before you is a massive raised pool, 15-ft tall and stinking of brine. Within the pool swims dozens, possibly hundreds, of illithid tadpoles, and amongst them lurks their community’s elder brain. A massive conglomeration of the brains of the dead, fused into one ghastly organism. The massive brain, is 10-ft long, flexible tendrils stretch from it.

Elder brains dwell in massive pools, not always raised, at least 15-ft in diameter and depth, if not more. This means that an elder brain will (almost) always be encountered submerged and attackers will be forced to deal with attacking across the water barrier and possibly even surmounting the 15+ foot wall of the pool; my studies suggest a disintegrate spell as a means of getting around these defenses in a raised pool. An elder brain has between 4 and 8 pseudopods capable of fine manipulations (reach 5-ft), but is physically almost defenseless, barely motile and unable to strike back at foes. Elder brains therefore rely upon guards and their telepathic powers to deal with attackers.

Elder brains exist partially on both the Prime and the Astral Plane. What the purpose of their Astral portion is I do not believe even the illithids know. What is known is that once an elder brain obtains its full size of 10-ft it stops growing on the Prime, instead expanding solely on the Astral Plane. Should an elder brain’s prime material body be slain its astral form continues to exist. I am only presenting game mechanics for their prime body at the present time, I may add their Astral body at a later time, possibly with stats for whether or not their Prime Material body has been destroyed. Certain of Marikus’s notes, that the illithids were initially unwilling to share, state that it was his belief that Ilsensine eats the eldest of the elder brains’ astral forms, and that given a critical mass of brains and age any and all elder brains would become gods and possibly merge into a single gestalt overdeity. Marikus, whose notes normally condemn Ilsensine and the elder brains, showed a single religious moment in response to this, a note of thanks to the Devourer of Secrets for his role in preventing the gestation of this overdeity. I cannot find the basis for Marikus’s beliefs, though, and they may have simply been more of his mad ravings.

Elder brains speak Common, Undercommon, and 7 other languages, but prefer to communicate telepathically.

Combat: An elder brain does not join combat willingly. To battle an elder brain requires that enemies make their way into the very heart of the illithid city. At this point the elder brain will send out a telepathic distress signal to all illithids within a mile, and then proceed to dispel any mental defenses their opponents may possess before releasing a powerful mindblast or psionic dominate to buy itself time for its guard to arrive. Elder brains are rarely found unguarded, brain golems and illithid usually standing ready to protect it.

Mindblast (Ps): This psionic attack is a cone 60 feet long or a burst 20-ft in radius. Anyone caught in this cone must succeed on a DC 24 Will save or be stunned for 3d4 rounds. The save DC is Charisma-based and includes Ability Focus. This ability is the equivalent of a 6th level power.
Psi-like Abilities:
Continuous (reactivation is a free action): Remote View Trap.
At-will: Dispel Psionics (+18 on dispel check), Id Insinuation (DC 22, 5 targets), Ego Whip (DC 24, 4d4 Charisma damage), Adapt Body, Attraction (DC 22, +9 bonus), Aversion (DC 22), Body Adjustment (6d12), Body Purification (6 points), Brain Lock (any type; DC 18), Control Sound, Create Sound, Demoralize (DC 22, 55-ft radius; may center at any point within 50-ft of its actual location), Detect Hostile Intent, Psionic Charm (DC 22, any type, 20 days), Psionic Dominate (DC 24, any combination of augmentations to reach up to 12 Power Points; so 3 humanoid targets for 1 hour, or 2 for 1 day, or 1 aberration, or 2 magical beasts, or a magical beast for 1 day, or a humanoid for 20 days), Psionic Suggestion (DC 22, 6 targets), Read Thoughts, Shatter Mind Blank, Telempathic Projection.
3/day: Hypercognition, Psionic Divination, any three Lv 7 or lower Telepathy, Psychoportation, Clairsentience, or Metacreativity powers (these 3 powers chosen from the Psion and/or Discipline lists upon creation; augmented to 13 PP).
All powers have a ML of 20, but are only augmented to a lower number of power points (usually 13).

Astral Distortion (Su): An elder brain’s presence disrupts the planar connections to the Prime nearby. Any planar travel (including summoning) within 120-ft of the Elder Brain is delayed by 5 rounds unless the Elder Brain chooses to allow it to pass through. Entities attempting to teleport into or out of the region, plane shift, or even move between the Prime and Ethereal Planes find themselves shunted from normal reality for the interval. The elder brain is aware of the number and kind of creatures entering or leaving this area, and where they are going to/from.

Blindsight (Su): An elder brain’s blindsight is psionic in nature and allows it to detect magic auras as Greater Arcane Sight, can penetrate illusions and transmutations as True Seeing within its area, and perceive the alignment of creatures within the area (unless concealed through magical effects).

Bud Brain Golem (Su): An elder brain is able to create brain golems. Doing so is a long and arduous process during which it may not use its Psi-like Abilities. An elder brain will normally keep 1 to 3 brain golems with itself at all time as guards.

Cyclopean Mind (Ex): An elder brain’s psyche is beyond that of normal mortals. An elder brain may treat itself as being in any square within 30-ft as the origin of any psi-like or spell-like ability it uses, and whether its bindsight has line of effect. An elder brain may use Intelligence in place of Dexterity to determine its Initiative. In addition it is immune to mind-affecting effects, and any creature attempting to affect it with a mind-affecting spell, spell-like ability, psionic power, mystery (even if Supernatural), utterance, or similar effect (whether a given Su ability qualifies is up to DM discretion) must make a Will save (DC 23; this DC is charisma based) or lose 4d6 power points and be stunned for 1 round, then confused for 1d4+1 rounds due to the psychic backlash, a creature confused by this effect treats itself as the caster of the confusion effect and can possibly be forced to attack or flee from itself.

Dual Existence: The majority of an elder brain actually exists on the Astral Plane. What is extent on the Prime is merely an extension. This astral portion is well hidden, resisting any divination attempts by beings with less than 11 divine ranks, and cannot normally enter other planes than the Astral. If slain on the Prime the Elder Brain’s consciousness fully re-enters the Astral Plane and it becomes unattached to the Prime. What happens to such an Elder Brain is unknown, probably madness.

Peer Through (Su): An elder brain is able to extend its senses through any willing or dominated creature within its telepathy range. While doing so it uses that creature’s senses, but gains the effects of True Seeing and Arcane Sight, and may Detect [Alignment] through the target. An elder brain may use this ability to see through up to 1 creature per point of Intelligence modifier (minimum 1).

Psionic Deflection (Su): An elder brain is surrounded by a field of psionic force which grants it a +4 Deflection bonus to AC and causes all ranged touch attacks to have a 40% miss chance against it.

Telepathy (Su): An elder brain’s telepathy extends for two miles in all directions through solid stone and other materials which would block line of effect. An elder brain may hold communications with up to 2 creatures per point of Intelligence modifier (minimum 1), and may serve to relay information between telepathic creatures within this area each pair counting as 1 creature communicated with. An elder brain is able to send out simple telepathic signals to any number of creatures at once but must either do so to all creatures with telepathy or all creatures with Int 1 or higher. Such signals are extremely limited in info being more general empathic feelings such as “danger” “fear” “hatred” “anger” “warning of ire”, etc.

Skills: An elder brain gains a +12 bonus to all Knowledge checks and may make Knowledge checks untrained.

[Zaydos]

Ok, this next one isn't quite a monster, but just something weird and a food source for illithids. The original version was a 2e thing from Legend of the Spelljammer but it never gained psionic power and I think capped at Int 6 instead of 25.

Brain Mold
Created by Marikus before his leaving illithid society, brain mold is a valuable boon to the illithids. This pale yellow mold is capable of growing in the underdark, decomposing organic matter and drawing nutrients out of the stone. In sufficient mass this mold obtains sentience (this requires 1000-ft square feet) and even psionic powers (1900 square feet). This mold is also capable of providing sustenance to illithids as if it were brains, assuming it was in a patch at least 500 square feet. It grows to a height of 3 inches and ~2 cubic feet can substitute for a brain in an illithid’s diet (one 5-ft square can feed 3 illithids). The brain mold’s flavor is proportionate to its intelligence. Non-intelligent brain mold, while fulfilling basic dietary needs, is completely flavorless and does little to sate the craving for brains. Even low intelligence mold is near flavorless and does little to curb these appetites. Fully sentient and psionically active brain mold is more filling, and some illithids even prefer it to thralls, but due to its lack of experience leaves something to be desired by the illithids. Even so many illithid cities will keep one or more patch of brain mold, kept controlled at just below or just above the level required for psionic awakening (the latter is potentially dangerous to thralls due to the chance of energy rays) as a supplemental or emergency food source. This mold is often used to feed illithid-kin (such as urophions, and kallipsids) and if brains are few the illithids themselves. All sustenance leaves the mold 1 day after separation from the mass, unless preservative means are taken (craft alchemy DC 25, or Preserve Organ spell from BoVD, or Gentle Repose). Illithids cultivate the brain mold primarily through the dumping of the bodies of their victims, thralls, or enemies, although some also have dedicated farmer thralls which will further fertilize it with more traditional fertilizers.

A creature capable of speaking with plants or telepathic communication can communicate with the brain mold but they do not have structures allowing them to naturally communicate either verbally or telepathically.

Mechanics
Brain mold is primarily an obstacle. It is an inanimate mold capable of only taking mental actions. Even so they have several creature like traits and is considered to have the plant type. Brain mold has an initiative modifier equal to its Intelligence modifier, and is allowed to make saving throws, with a Fort save modifier of +1 per 500 square feet (i.e. 3 10-ft squares) of brain mold beyond 1000-ft, and the same bonus to Will saves but increased by their Wisdom modifier, but it automatically fails Reflex saves. Brain mold is immune to weapon damage, although an area of effect that deals at least 10 points of damage will destroy all the mold in its area, and a source of fire damage dealing at least 5 points of damage will destroy the mold in a single square. Prolonged contact with flame (alchemist fire or holding a torch to the brain mold) will cause it to catch aflame the fire spreading to all adjacent squares each round till extinguished. An area of effect that deals at least 10 Con damage will also slay brain mold and for area of effect death effects the brain mold is considered to have 1 HD +1 HD per 500 square feet past 1000-ft and blindsight out to 10-ft per effective hit die. A power word (or other effect based on hp) affects a patch as if it had 10 hp per effective hit die. Brain mold is immune to spell effects that target a specific number of creatures except those that deal fire damage (which can destroy a 5-ft square per target) and mind-affecting effects (but is immune to mind-affecting effects due to being considered a plant). Patches of brain mold do not need to be contiguous, as long as the nearest points between two patches are separated by no more than 6 squares (and have line of effect) they are considered one patch. Brain mold has an Int score of 5 if it has at least 1000-ft (40 5-ft squares), +1 per 100-ft (4 5-ft squares) beyond that up to 1500 ft (60 5-ft squares). Beyond that it increases by +1 per 200 ft (8 5-ft squares) up to 2500 ft (100 5-ft squares), then +1 per 500 ft (20 5-ft squares) beyond that up to 5000 ft (200 5-ft squares), and then +1 per 1000 ft (40 5-ft squares) up to 10000 ft (400 5-ft squares), beyond that size there has been no noted increase in their Intelligence. Brain mold’s Charisma is equal to its Intelligence up to 1500 ft and beyond that increases by 1 per 2 points above 10 its Intelligence is. Brain mold’s Wisdom is 10 + 1 per 2 points above 10 its Intelligence has reached. Brain mold with an Int above 10 is capable of using psionics as a seer (psion). Their seer level is 3/4 per point above 10 their Intelligence reaches rounded down (so at Int 12 they are a 1st level seer and at Int 18 as a 6th level seer, and at 25 Int they are considered to be an 11th level seer). A patch of brain mold targeting itself with a psionic power may affect its entire mass, but any effects which originate from its form treats 1 10-ft square as its form (so energy burst would be centered on one 10-ft square not the entire 25+ 10-ft squares that make it up). A patch of brain mold capable of manifesting psionic powers gains 1 feat + 1 feat for 3 effective seer levels. If part of a patch is destroyed it takes 1 minute before the resulting loss of intelligence is felt by the mass.

For example a patch of brain mold covering the floor, walls, and ceiling of a 30-ft by 30-ft by 30-ft chamber would cover 216 5-ft squares (a 30-ft by 30-ft room has a floor of 6 by 6 squares if it is also 30-ft high it is a cube with 6 faces each 6 by 6, 6^3 = 216) or 5400 square feet. This would give it an Int of 20, Wis and Cha of 15, effective seer level of 7, +10 Fort, +12 Will, and an effective 11 hit dice for effects that register hit dice, 110 hp for power word style spells, and 110-ft blindsight. If a wizard cast fireball position in one of the corners of the room it would destroy all the brain mold in its area (33 5-ft squares of it, or 825 square feet) and a more intelligent position would be one 20-ft from a corner along the edge of the floor or ceiling and a wall or two walls (it would destroy a 10-ft square on one wall/floor/ceiling and 22 on each of the others for 48 5-ft squares destroyed, or 1200 square feet). Regardless of which choice you made the brain mold would not feel the resulting intelligence loss for 1 minute and would during that period retain its full Lv 7 psion powers. If you retreated and returned 1 minute later you would find a rather angry Lv 6 seer with an Int of 18 or 19 depending upon where you targeted. If while you were fleeing the fighter dropped a flask of alchemist fire in a corner it would have destroyed the initial square, then each square adjacent to it, then so forth. Assuming you hadn’t fireballed things (for simplicity) it would have destroyed 1 square, then 3 by 3 squares, then 5 by 5, 7 by 7 (if left in the middle of the floor the entire floor would be gone and the bottom 5 feet of each wall), 9 by 9 (in the above the bottom 10-ft of each wall would be gone), 11 by 11 (15-ft), 13 by 13 (20-ft), 15 by 15 (25-ft), 17 by 17 (entire walls) and 2 more rounds would destroy the entire patch. Your pyromania has also killed an innocent life form, and force illithids to eat 1350 brains they weren’t going to have to.

[Zaydos]

Elder Brain, Wight
Large Undead (Psionic)
Hit Dice: 15d12+30 (117 hp)
Initiative: +5
Speed: 10 ft (2 squares), swim 15 ft.
Armor Class: 20 (-1 size, -2 Dex, +8 natural, +5 deflection), FF 20, touch 12.
BAB/Grapple: +7/+13
Attack: Tentacle +8 melee (1d6+2 and energy drain)
Full Attack: 4 Tentacles +8 melee (1d6+2 and energy drain)
Space/Reach: 10 ft/5 ft (15 ft with tentacles)
Special Attack: Energy Drain, Mindblast, Psi-like Abilities
Special Qualities: Blindsight 120-ft, Darkvision 60-ft, DR 10/magic and good, Psionic Deflection, Schismed Mind, Spell Resistance 25 (14 + CR), Telepathy (1000 ft)
Saves: Fort +5, Ref +3, Will +13.
Abilities: Str 14, Dex 7, Con -, Int 21, Wis 18, Cha 21
Skills: Bluff +23, Concentration +23, Intimidate +25, Knowledge (any 3) +29, Knowledge (any other) +11, Sense Motive +24, Spellcraft +23
Feats: Ability Focus (Mind Blast), Improved Toughness x2, Life Drain, MindsightLom, B, Quicken Psi-like Ability (Stygian Ray)
Environment: Any land or underground
Organization: Solitary, or plague (2-12 illithid vampires and 1 wight elder brain)
Challenge Rating: 11.
Treasure: Standard.
Alignment: Always Chaotic Evil
Advancement: 16-20 HD (Large), 21-40 HD (Huge)
Level Adjustment: –
A great brain approaches you, pulling itself forward with a dozen small tendrils of. A conglomeration of pale grey matter, half shriveled, it towers almost 8-ft in diameter, its mind already brushing against yours.

A wight elder brain is the result of when an elder brain is slain through energy drain, or its corporeal body is reanimated through a special ritual used with Create Greater Undead (discovering this ritual could be a quest, or as simple as a DC 30+ Knowledge Arcana or Dungeoneering check). When an elder brain rises this way they lose some of their volume and mass, their body shriveling and shedding water. They also lose their place in the illithid community, turning from bastions of that order to reaving terrors. A wight elder brain develops a hunger for fresh brains, which it removes from the dead to add to its form, eventually regaining the size lost in its reanimation and more. A wight elder brain prefers illithid brains to all others, psionic brains to non-psionic ones, and greater intelligence to lesser intelligence.

Just because a wight elder brain is now driven by an unrelenting hunger for brains does not mean they are always solitary creatures. They find solace in fellow undead illithids, surrounding themselves with retinues of illithid vampires out of vanity, or even allying with powerful alhoons. Those wight elder brains unable to gather an undead retinue instead prowl the underdark alone, hunting their former kin and other sentient creatures of the realm killing them and adding their brains to its mass. A wight elder brain will wipe out sentient life in the region before moving on, growing as it kills.

Combat: A wight elder brain usually begins combat with a quickened stygian ray to inflict a minor penalty to a target’s saving throws and follows it up with a mindblast to immobilize foes and then moves forward to energy drain targets. They will follow up by using Stygian Bolt and their Energy Bolt powers on foes that resist their initial assault, using Dispel Psionics to strip foes of their protection to energy drain if any.

Energy Drain (Su): A creature struck by a wight elder brain’s tentacle attack suffers 1 negative level. A wight elder brain can inflict up to 4 negative levels this way a round. The Fort DC to remove these negative levels is 22 (this DC is Charisma based). When a creature suffers this energy drain they lose an additional 5 hit points with each negative level (for a total of 10) and the wight elder brain gains 10 temporary hit points (for 1 hour) each time it inflicts a negative level due to its Life Drain feat.

Mindblast (Ps): This psionic attack is a cone 60 feet long or a burst 20-ft in radius. Anyone caught in this cone must succeed on a DC 22 Will save or be stunned for 3d4 rounds. The save DC is Charisma-based and includes Ability Focus. This ability is the equivalent of a 5th level power. Once a wight elder brain uses its mindblast it cannot use it for another 1d4 rounds.

Psi-like Abilities: 1/day: Psionic Dominate (DC 21, ML 11, various possible advantages), Stygian Bolt (Ref DC 21; ML 11), any one 5th level or lower Psion power (ML 9). 3/day: Dispel Psionics (+17 on dispel check), Energy Bolt (DC 20, 9d6 + energy type modification), Ego Whip (DC 19, 2d4 Charisma damage), Psionic Dimension Door, Psionic Suggestion (DC 17, 4 targets). At-will: Aversion (DC 20), Demoralize (DC 20, 50-ft radius), Mental Disruption (DC 20 and 10-ft, DC 19 and 15-ft, DC 18 and 20-ft, or DC 17 and 25-ft), Read Thoughts, Stygian Ray (ML 11, 3/day as a swift action). Manifester Level is 9 except where noted otherwise.

Blindsight (Su): A wight elder brain’s blindsight is psionic in nature and allows it to detect magic auras as Detect Magic.

Psionic Deflection (Su): An elder brain is surrounded by a field of psionic force which grants it its Charisma modifier as a Deflection bonus to AC and causes all ranged touch attacks to have a 40% miss chance against it.

Schismed Mind (Ex): A wight elder brain’s psyche is capable of directing both its psionic powers and physical body simultaneously with ease. 1/round a wight elder brain may use one of its psi-like abilities (including Mind Blast) as a free action instead of a standard action.

Telepathy (Su): A wight elder brain’s telepathy extends for a 1000 feet in all directions through solid stone and other materials which would block line of effect. A wight elder brain may hold communications with up to 2 creatures per point of Intelligence modifier (minimum 1), and may serve to relay information between telepathic creatures within this area each pair counting as 1 creature communicated with. A wight elder brain is able to send out simple telepathic signals to any number of creatures at once but must either do so to all creatures with telepathy or all creatures with Int 1 or higher. Such signals are extremely limited in info being more general empathic feelings such as “danger” “fear” “hatred” “anger” “warning of ire”, etc.

Skills: An elder brain gains a +6 bonus to all Knowledge checks and may make Knowledge checks untrained.