Large Aberration, Lawful Evil
Armor Class 18 natural armor
Hit Points 221 (26d10 + 78)
Speed 10 ft., swim 40 ft.
STR
21 (+5)
DEX
10 (+0)
CON
17 (+3)
INT
27 (+8)
WIS
18 (+4)
CHA
21 (+5)
Saving Throws CON +9, INT +14, WIS +10, CHA +11
Skills Arcana +20, Deception +12, History +20, Insight +10, Perception +16, Persuasion +12, Stealth +6
Damage Resistances Psychic
Senses Darkvision 120 ft., Passive Perception 26
Languages All, Telepathy 2 miles
Challenge 17 (18,000 XP)
Proficiency Bonus +6

Amphibious. The ibyoleth can breathe air and water.

Innate Spellcasting (Psionics). The ibyoleth's innate spellcasting ability is Intelligence (spell save DC 22). It can innately cast the following spells, requiring no components:
At will: detect thoughts (range 2 miles), levitate 
3/day each: dominate monster, telekinesis, modify memory
1/day each: legend lore, plane shift (self only)

Magic Resistance. The ibyoleth has advantage on saving throws against spells and other magical effects. 

Mucous Cloud. While underwater, the ibyoleth is surrounded by mind-rending mucus. A creature that touches the ibyoleth or that hits it with a melee attack while within 5 feet of it must succeed on a DC 22 Constitution saving throw or take 1d10 psychic damage and have disadvantage on the next saving throw they make. 

Probing Telepathy. If a creature communicates telepathically with another creature while within 2 miles of the ibyoleth, the ibyoleth can listen into their conversation, and learns the exact position of both creatures while they are within 2 miles of the ibyoleth. 

Knowledge Hub. The ibyoleth automatically casts detect thoughts on a creature that communicates with it telepathically (no action required). If the creature fails their saving throw against the spell when the ibyoleth attempts to learn more about the creature, the ibyoleth learns all the knowledge that they know. This include, but is not limited to all of their thoughts, fears, memories, hopes, and experiences. If the ibyoleth communicates telepathically with an aberration that has telepathy, they can share any or all of the knowledge that they have compiled mentally from any specfic creature, taking a minute per creature. 

Actions

Multiattack. The ibyoleth makes two tentacle attacks, or one attack with its tentacle and one with its Extract Brain.

Tentacle. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage plus 19 (2d10 + 8) psychic damage. If the target is Large or smaller, it is grappled (excape DC 22) and must succeed on a DC 22 Intelligence saving throw or become stunned until the grapple ends. The ibyoleth has four tentacles, each of which can grapple a separate creature. The ibyoleth can choose to move a grappled creature to any space within 5 feet of itself as part of this attack.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (3d6 + 5) bludgeoning damage.

Extract Brain. Melee Weapon Attack: +14 to hit, reach 5 ft., one incapacitated creature with a brain that is grappled by the ibyoleth. Hit: 82 (15d10) piercing damage. If this damage reduces the target to 0 hit points, the ibyoleth kills the target by extracting and consuming their brain, as well as learning all knowledge the deceased creature did. 

Enslaving Blast (3/day). The ibyoleth magically emits a psychic burst of enslaving energy in a 120-foot cone. Each creature in that area must succeed on a DC 22 Wisdom saving throw or become charmed by the ibyoleth until they are no longer on the same plane of existence, or the ibyoleth dies. While charmed this way, the creature can't take reactions, and can telepathically communicate with the ibyoleth from any distance. The charmed creature does as the ibyoleth commands it, but will do any suicidal activities. 

Whenever the charmed creature takes damage, it can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can rpeeat the saving throw when it is at least one mile away from the ibyoleth. The ibyoleth can choose to end this condition as a reaction. When the condition ends in any way, the previously charmed creature takes 34 (4d12 + 8) psychic damage.

Legendary Actions

The ibyoleth can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The ibyoleth regains spent legendary actions at the start of its turn.

Detect. The ibyoleth makes a Wisdom (Perception) check.

Tail Swipe. The ibyoleth makes one tail attack.

Psychic Drain (Costs 2 Actions). One creature charmed by the ibyoleth takes 10 (3d6) psychic damage, and the ibyoleth regains hit points equal to the damage the creature takes.

Description

In the rare occasion that an aboleth that is captured by a mind flayer colony, and they somehow manage to transport it back to their base of operations, they can inject a large mind flayer tadpole into its skull, and cause it to undergo ceremorphosis. This process goes very differently in the mind of an aboleth than it typically does, due to the anatomical and mental differences between an aboleth and a humanoid. This change is likely to go awry, resulting in the death of both the tadpole and aboleth. If the transformation is completed, the aboleth will change in physical appearance significantly. 

The most noticable change after the process of ceremorphosis is the color change. A typical aboleth can range from a pale sky-blue to a whitish green. After the change into a mind flayer, an ibyoleth is a glimmery, rich purple color, about the shade of an eggplant. Their tentacles transform into sucker-colored illithid tendrils that they use to grab their prey and devour their brains. Their mucus cloud is a pale pink color that coats their whole body while underwater. Their alien mouths change to become more circular, almost a perfect large replica of an illithid's mouth. 

The metamorphosis into an ibyoleth does not only change an aboleth physically, though. The most notable change is their mental capacity, an ability that all illithids, even elder brains, envy. Due to the physical structure of an aboleth, their brain runs all the way down their spine, ending near the bottom of their tail. This massive brain is consumed by an illithid tadpole during ceremorphosis, who has to grow to replace this whole monstrous organ. This greatly enhances and twists both the psionic capabilities of aboleths and illithids, blending them together. This lends them a few handy abilities, such as the ability to enslave people with a burst of psychic energy, or the ability to transverse the planes how mind flayers can. 

Another feature that ibyoleths possess is their ability to hold memories of others that they communicate with telepathically. They are capable of absorbing all the memories of creatures they interact with in a telepathic manner, learning everything that they know and have experienced. They can also communicate any of the knowledge they know with their allies, functioning as a living archive of everything the hive has ever experienced. This is unique to ibyoleths, and is why all other mind flayers are jealous of them. This comes from their perfect memories, which they inherited from their aboleth bodies. 

Because of all of these unique abilities, an ibyoleth is both treasured and despised inside of a mind flayer colony. Whenever a mind flayer feeds on a creature's brain, if the colony has an ibyoleth, they will journey back to their base and speak telepathically with the ibyoleth, so that it can compile and organize memories and knowledge that they have learned from the brains of those they devour. They do this to learn more about the behaviors of other creatures, to search for any lost lore that they would wish to know, and learn as much about the world as they possibly can, with the off chance that they may learn a forgotten secret (such as how to create a Nautiloid). 

An ibyoleth who has access to a great supply of information can learn enough about humanoids and their other prey to perfectly predict the actions of individuals and societies in a variety of circumstances. For example, an ibyoleth that live in a colony near an orc tribe could use their telepathy to pretend to be Gruumsh, saying all the key phrases needed to provoke their rage, which they could use to drive off a nearby rival mind flayer colony or other enemy, without risking the lives of their own colony's members in any way. Due to this vast mental toolset, an ibyoleth will often be the core member of a mind flayer colony, the advisor to the elder brain. 

Though an ibyoleth is more powerful and intelligent than an elder brain, they are normally more than willing to cooperate with the colony leader and allow it to take the lead. Elder brains possess abilities that even the ibyoleth doesn't contain, and without an elder brain or ulitharid, a colony is normally severely lacking. In the event of a colony split, the half that contains the elder brain will always keep the ibyoleth in their base. An elder brain and an ibyoleth that cooperate together can become bonded, the closest thing in a mind flayer society to a friend, the concept of which is completely alien to illithids. 

Lair and Lair Actions

Lair Actions

When fighting inside its lair, an ibyoleth can invoke the ambient magic to take lair actions. On initiative count 20 (losing initiative ties), the ibyoleth takes a lair action to cause one of the following effects:

  • The ibyoleth casts phantasmal force (no components required) on any number of creatures it can see within 60 feet of it. While maintaining concentration on this effect, the ibyoleth can’t take other lair actions. If a target succeeds on the saving throw or if the effect ends for it, the target is immune to the ibyoleth's phantasmal force lair action for the next 24 hours, although such a creature can choose to be affected.
  • Pools of water within 90 feet of the ibyoleth surge outward in a grasping tide. Any creature on the ground within 20 feet of such a pool must succeed on a DC 14 Strength saving throw or be pulled up to 20 feet into the water and knocked prone. The ibyoleth can’t use this lair action again until it has used a different one.
  • Water in the aboleth’s lair magically becomes a conduit for the creature’s rage. The ibyoleth can target any number of creatures it can see in such water within 90 feet of it. A target must succeed on a DC 14 Wisdom saving throw or take 7 (2d6) psychic damage. The ibyoleth can’t use this lair action again until it has used a different one.

Regional Effects

The region containing an ibyoleth's lair is warped by the creature’s presence, which creates one or more of the following effects:

  • Underground surfaces within 1 mile of the ibyoleth's lair are slimy and wet and are difficult terrain for non-abberations.
  • Water sources within 1 mile of the lair are supernaturally fouled. Enemies of the ibyoleth that drink such water vomit it within minutes. The ibyoleth and all aberrations of its choosing can drink the water with no complications.
  • As an action, the ibyoleth can create an illusory image of itself within 1 mile of the lair. The copy can appear at any location the ibyoleth  has seen before or in any location a creature charmed by the ibyoleth can currently see. Once created, the image lasts for as long as the ibyoleth maintains concentration, as if concentrating on a spell. Although the image is intangible, it looks, sounds, and can move like the ibyoleth. The ibyoleth can sense, speak, and use telepathy from the image’s position as if present at that position. If the image takes any damage, it disappears.

If the ibyoleth dies, the first two effects fade over the course of 3d10 days.

Monster Tags: Mind Flayer

Environment: UnderdarkUnderwater

The_Leviathan_of_Levistus

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