Mind flayer

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The mind flayer, h, is an especially perilous type of monster that appears in NetHack. They are omnivorous humanoids with octopus-like tentacled heads, and possess flight, telepathy, see invisible, and infravision. The mind flayer can use its tentacle attacks to eat its victims' brains, draining intelligence and abusing wisdom while often inflicting amnesia - losing enough intelligence this way can be irreversibly fatal.

A mind flayer can grow up into a master mind flayer, h; both share a colored glyph with the dwarf king, h. Eating their corpses can grant telepathy or raise intelligence by 1 point, with a 50% chance of each.[1]

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Mind flayer tentacle attacks no longer cause amnesia.

Other common traits

Mind flayers move at the same speed as an un-hasted, unburdened player character and can wear all armor. They will occasionally concentrate and release a blast of psychic energy, and can sense if you have telepathy yourself—"a faint wave of psychic energy" is a sign that one is present on the level. If you have telepathy and are within sight or telepathy range of a mind flayer, it will cause a wave of psychic energy to pour over you - a mindflayer that is hostile or under the effects of conflict will "lock on" to your mind or telepathy for d15 damage, which is affected by half spell damage; a peaceful or tame mind flayer will attack other monsters the same way, but also produces "soothing" energy that is harmless to you.


Randomly-generated mind flayers and master mind flayers are always generated hostile. They are also valid polymorph forms, meaning that you may encounter one far earlier in the dungeon either as the guise of a shapeshifter or the result of a polymorph trap.

Both types of mind flayer are notorious for potentially generating upon entering a floor of the Gnomish Mines, where they are normally far too high difficulty to appear. These "minesflayers" are the result of the Mines levels specifying that one random humanoid (h) monster should be generated at normal level creation; this is almost always a dwarf, hobbit, or bugbear. On occasion however, the function that chooses which humanoid monster should be generated totally ignores the difficulty of the monster it produces and creates a (master) mind flayer.


The mind flayer has a base AC of 5, and is likely the variety a player will encounter first.

The master mind flayer has a base AC of 0 and a stronger weapon attack, along with 5 tentacle attacks; it is otherwise identical to its previous form in many aspects.


In addition to the above, master mind flayers can be summoned by the summon nasties monster spell.


Mind flayers and master mind flayers are considered a consistent, high-level threat throughout the entirety of the game due to the intelligence-draining attack, which has taught many an unfortunate lesson to players. Brainlessness is an instadeath that ignores not only your current HP, but lifesaving as well—you will be brought back, only to immediately die again since your brain is still gone. If you die from intelligence drain while polymorphed, you will also permanently die instead of reverting to your normal form. This makes mind flayers and their 'master' forms common targets for genocide, as well as stellar pets for those who can procure a tame flayer.

If in explore mode or wizard mode and you choose not to die of brainlessness, your intelligence is then boosted by two points.[2]


If you start sensing waves of psychic energy, that is your cue to farlook and check whether any h you encounter is a dwarf—a somewhat common YASD is to mistake the mind flayer for an easier-to-kill dwarf king, then march in and have your brain promptly eaten. If you have telepathy, blinding yourself temporarily (e.g., via blindfold or towel) can be used to quickly confirm if a flayer is present on a level; dwarves also do not generate randomly inside Gehennom, making detection there more trivial.


When fighting mind flayers, avoid melee-range combat if at all possible, especially if you are burdened and/or have low intelligence. Mind flayers respect Elbereth and can be deterred by standing on a scroll of scare monster, though the former will not work in Gehennom. A flayer's 90 MR will often resist many of the spells that manage to hit through their AC, and makes scaring them through other means a difficult task.

An expensive camera or tooled horn, while not as secure as Elbereth for the above reasons, can still frighten off mind flayers, especially in Gehennom where Elbereth is of no use. Beware that a fleeing mind flayer may still attack you, although it is much less likely to; additionally, a blinded one will not respect Elbereth. Scaring a mind flayer also does not prevent them locking on to your mind or telepathy.

Cancellation will not affect their brain-sucking attacks even if it successfully hits; projectiles such as daggers or arrows are among your best resources to consistently deal damage. Alternately, if your ranged attack options are limited and melee is your only out, consider stoning them or taking other measures to prevent or minimize stat loss (discussed in more detail below).

Preventing intelligence drain

Wearing any greased helm prevents the mind flayer's tentacles from reaching your brain, but the grease has a 12 chance of wearing off with each attack; a non-greased helm has a 78 chance of preventing each of the mind flayer's tentacle attacks. Mind flayers get multiple attacks per turn, so you should not rely solely on a greased helm, especially if you are unable to kill them quickly. Alternate possibilities include wearing a dunce cap or ring of sustain ability; both items will fix your intelligence stat (either at 6 or its current value), preventing stat loss and thus brainlessness, on top of the dunce cap's chance of blocking the tentacles. A blessed unicorn horn or potion of restore ability can also reverse the stat loss fairly quickly.

Polymorphing into a headless monster will protect you from the intelligence drain attacks, which can mitigate the worst of their threat;[3][4] polymorphing into a normally mindless form will not protect you - as a comment in the relevant code says, players aren't mindless.[5][6]

None of these methods will prevent amnesia from a successful brain-sucking, and you're likely to come out of the fight very forgetful—have a means of re-identifying items on hand if possible. You can use #name to label one of a particular type of item(s) that you consider vital and/or does not auto-identify as a precaution.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

In addition to mind flayer attacks no longer causing amnesia, unicorn horns will no longer restore lowered stats.


While the amnesia and instadeath from brain-eating are enough to make both forms of mind flayer a popular target for genocide, do not attempt blessed genocide of mind flayers if you are a dwarf! Using a blessed scroll of genocide will remove all h from the current game including dwarves, serving as a particularly aggravating YASD for forgetful dwarven players.

One or two "normal" genocides, either from the uncursed scroll or a throne, should be used instead; the master mind flayer should ideally be targeted first, as regular mind flayers cannot be generated via summon nasties unless they randomly replace an extinct/genocided nasty.

You should ideally always identify the beatitude of possible scrolls of genocide before reading, but this is especially true if you plan to eliminate mind flayers with one—that randomly read scroll you just found may be cursed, and the summoned horde of mind flayers will often result in a quick death, and even if you can scare them away, their psychic blasts may still overwhelm you. Also, be sure to mind your spelling, especially if you are a Monk—misspelling it as "master mindfalyer" will only parse the word "Master", one of the Monk's rank titles, and wipe out all monks including you.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

If a genocided monster with a pre-grown form (that is not explicitly a baby form) is chosen, and this form is not also genocided, it will appear in place of the genocided monster. For example, mind flayers can appear in place of genocided master mind flayers. This also happens if the chosen nasty is inappropriate for the location, such as an arch-lich outside Gehennom.

As pets

While highly desirable as pets, taming a mind flayer is extremely hard and dangerous due to their monster magic resistance; you may be much better off using a polymorph trap on your current pet. Tame mind flayers make quick work of shopkeepers, and their telepathic outreach only locks onto and damage hostile monsters - the harmless message it otherwise produces can be hidden with MSGTYPE. Remember that only tame and peaceful mind flayers will generate soothing psychic waves—if you see different messages related to psychic waves, are taking damage from them, and you are not generating conflict, then a hostile mind flayer may be on the level.

Be especially careful if your tame mind flayer becomes confused—they will turn those psychic waves on you! This also makes conflict similarly perilous. However, mind flayers' high monster magic resistance ensures that once it reaches level 15, they will become immune to conflict - and thus no threat to you or your brain matter - should you decide to use it.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Per this commit:

The chance of resisting conflict now depends on the player's charisma, the monster's level, and the player's level. Conflict is resisted if rnd(20) > min(19, (ACURR(A_CHA) - mtmp->m_lev + u.ulevel)) - thus, there is always at least a 5% chance of resisting it. Conflict also now requires that the monster see the player, not that the monster be in the player's line of sight. These changes are imported from SporkHack.

Tame flayers excel at killing many other monsters due to their tentacle attacks: non-mindless monsters take an additional d10 of damage per brainsucking attack to simulate brain loss.[7] However, there are a few monsters that in turn pose a serious threat should a mind flayer attempt to eat their brain:

  • Cockatrices, chickatrices and Medusa will turn a mind flayer to stone if a tentacle attack lands.
  • Jellies have passive attacks that can easily rack up enough damage to kill an unlucky mind flayer attacking one.
  • Shapeshifters and green slimes are similarly dangerous: the former may go down quickly, but will polymorph a mind flayer that eats its corpse, while the latter is extremely likely to turn it into another slime.
  • Riders that mind flayers target are immediately fatal if they manage to eat one's brain, though the Rider in question still takes the extra "brain loss" damage.[8]

Ochre jellies are a common sight in the late game, especially as a summonable nasty—consider giving your mind flayer any yellow dragon scales (or dragon scale mail) that you happen upon to provide them with valuable acid resistance.

Mind flayers also have a tendency to attract covetous monsters with their psychic blasts; if approaching the goal level of your Quest, the Wizard of Yendor's Tower or one of the many demon lairs of Gehennom, you may want to leave them on another floor temporarily. Alternately, if you intend to draw covetous foes to the stairs this way, be prepared accordingly; in particular, a mind flayer pet or polyform can be used by Rogues on their quest to awaken the Master Assassin, who will then warp to you from his otherwise inaccessible dwelling.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

From commit 0891ef4: Monsters wearing alchemy smocks now additionally gain acid resistance instead of just poison resistance, allowing for more flexibility in kitting out a tame mind flayer. Additionally, per commit 2cad4ec, each individual covetous monster will pick either the upstairs or downstairs to warp to.

As a polymorph form

The master mind flayer is a very sought-after form for polyself: on top of flight, multiple attacks per turn, 0 base AC of 0 and no changes to armor or encumbrance, its brain-eating attack is deadly to nearly anything. When eating a monster's brain, you gain d30 nutrition per successful tentacle attack and exercise wisdom, without risk of choking; if your intelligence is below its current maximum (e.g., your own brain was sucked), it will be increased by d4.[9] The intelligence increase is subject to the normal polymorphed attributes rules, and will be reset when you revert to your normal form; among its few drawbacks are that your max HP may also drop significantly in this form, especially if polymorphing at a high level. The master mind flayer form also sees use in speed ascensions, especially with physically-weak elven Wizards.

Naturally, players in mind flayer form face the same dangers as pet mind flayers, including potential death from triggering too many passive attacks. Furthermore, brainsucking a green slime causes delayed sliming, and eating a cockatrice's brain causes both immediate stoning and delayed stoning if the immediate stoning was stopped by an amulet of lifesaving. Sucking the brains of your race or other mind flayers will count as cannibalism as well, though this does not trigger a penalty for each individual brain-sucking attack[10] - for Monks and vegan or vegetarians players, eating brains will also break those conducts. While you cannot choke directly from eating brains, you can become satiated—you will not receive a warning when oversatiated, and thus run a significant risk of choking from eating anything afterward, which is an instadeath even while polymorphed.


The mind flayer first appears in NetHack 3.1.0, and the master mind flayer is introduced in NetHack 3.3.0.

From 3.1.0 to NetHack 3.4.3, including some variants based on them, the game would not recognize the alternate spelling "mindflayer" when selecting a monster for genocide. This meant that from 3.3.0 to 3.4.3, a Monk that attempted to genocide "master mindflayer" would instead genocide "master", thus wiping out all Monks and ending the game. As mentioned above, "master" is one of the rank titles for Monks, and the parser ignored the 'unfamiliar' word "mindflayer";[11] this was fixed in NetHack 3.6.0.

Master mind flayers are one of the many polyforms that can aid in pudding farming in earlier versions of the game where it was possible.


Mind flayers are derived from Dungeons & Dragons, where they appear in all editions and were also known as illithids; the illithid is considered "Product Identity" by Wizards of the Coast, and as such is not released under its Open Game License. Dungeons & Dragons co-creator Gary Gygax stated that one of his inspirations was the cover painting of the Titus Crow book The Burrowers Beneath by Brian Lumley. The first mention of illithids is found in the first issue of TSR Games' official newsletter The Strategic Review; they were included in the Eldritch Wizardry supplement for the original white box edition of the 1976 Dungeons & Dragons game, where they were depicted as Lawful Evil; they also appear in the first edition's Monster Manual; and the 3rd and 3.5 editions introduce playable illithids.

The illithid is "a super-intelligent, man-shaped creature with four tentacles by its mouth which it uses to strike its prey"; a tentacle that hits penetrates to the brain and draws it forth, allowing the monster to devour it. Its major weapon is the 'mind blast', a short-range wave of "PSI force" which affects each opponent differently based on how intelligent it is, and can induce many ailments from confusion and insanity, up to coma and even death. In-universe, the origins of the illithids are subject to many conflicting stories.

Illithid society is structured around a creature called an "Elder Brain", which lives in a pool of cerebral fluid in the center of a city. Dead illithids have their brain extracted and taken to this pool to have its contents absorbed, which illithids believe a form of immortality; this Brain also functions as a vast library of knowledge that an illithid can call upon with a simple telepathic call. Psionic potential is thus an integral part of the illithid identity, and they typically communicate by projecting thoughts and feelings to each other.

While illithids do have a patron deity known as Ilsensine, few of them actively worship her - both because they believe themselves the most powerful creatures in the universe, and because Ilsensine is more of an "abstract" deity that represents universal knowledge and one’s mastery of their own mind, a state that all illithids seek. Outcast illithids that turn to wizardry are often known to become alhoons.


The <master> mind flayer's tentacles suck you!
A mind flayer has hit you with its brain-sucking attack.
Your brain is eaten!
You lost intelligence and/or memory of items and floors to the brain-sucking attack.
Your <helm> blocks the attack to your head.
Your worn helmet successfully protected you from its tentacle attack.
You don't seem harmed.
You were protected you from the tentacle attack due to being in the form of a headless monster.
Your last thought fades away.
You died of brainlessness.
<Foo>'s brain is eaten!
A monster was hit by a mind flayer attack, and takes an extra d10 damage.
<Foo> doesn't notice.
As above, but the 'victim' was mindless and takes no extra damage.
<Foo>'s last thought fades away...
A monster was killed by the brain-sucking attack.
Ingesting that is fatal.
You ate the brain of a Rider while in mind flayer form, dying instantly and abusing wisdom if you are revived by an amulet of life saving.[12]
You have a sad thought for a moment, then it passes.
A tame mind flayer was turned to stone from an attempt to eat a monster's brains.

Variants and patches

In the Heck² patch, one of the possible special levels in the "heck-a" list is filled with mind flayers and master mind flayers.

In the Lethe patch, the Wizard's Manse map for the fifth floor of the Lethe Gorge has a throne room with three thrones occupied by a sleeping master mind flayer and two sleeping mind flayers; the master mind flayer generates with a wand of cancellation, while one mind flayer generates with a wand of lightning and the other generates with a wand of sleep.


Mind flayers and their master forms are somewhat different in SLASH'EM. The master mind flayer has three brain-eating attacks, while the normal mind flayer has five—this is an unusual reverse of the situation in vanilla NetHack. More importantly, the ring of free action provides Luck-based protection against their brain-eating attacks, starting at a 50% of blocking each individual flay and increasing to a 90% chance at maxed-out Luck.[13] This, in combination with a greased helm, renders them somewhat less of a threat.

While genociding mind flayers is still generally a worthwhile idea, there are more sources of amnesia present such as the potions of amnesia and the migo queen's attacks, making it much less reliable as a preventative method against amnesia specifically.

Both mind flayer polyforms are incapable of wearing helmets due to tentacle placement, but can still wear all other armor. In addition, SLASH'EM makes it so that any additional bite or tentacle attacks that would automatically process and result in death (e.g. by attacking a cockatrice) are simply not used; this does not apply to the weapon attack, so as always be mindful of fighting bare-handed.

In the Lawful Quest, the locked chamber in the middle of the Cloud Bank has a chance of housing mind flayers known as the "Spice Girls": one named Ginger is guaranteed to appear, while two others named Victoria and Emma each have a 45 chance of generating. They may be accompanied by two master mind flayers named Mel B. and Mel C., who each have a 35 chance of being generated. Ginger is generated on top of a fountain and a chest that has a wand of cold with 16 charges; the chest also has a 710 chance of containing an amulet of flying, and a 45 chance of containing a wand of digging, making it a possible boon for sufficiently tough players. If either type of mind flayer is genocided, they will be replaced by random monsters with the same names.

SLASH'EM recognizes the "mindflayer" spelling, so it is okay to genocide "master mindflayer", but a typo like "master mindfalyer" will still wipe out all Monks (including you if you are one).


In dNetHack, mind flayers and their master kin are considered primordials. dNetHack also adds parasitic mind flayers and parasitic master mind flayers as well as alhoons, master mind flayers that have turned to lichdom.

The Drow Noble Quest involves infiltrating a colony of mind flayers and retrieving the quest artifact, the Web of the Chosen; there are 16 mind flayers and 2 master mind flayers scattered about the goal level around the elder brain, with the brain guarding the Bell of Opening. The quest artifact's actual owner, A'gone, is locked up in a cell on the edge of the level, with her mind completely gone due to the mind flayers.

Anachrononaut quest

The Anachrononaut quest features mind flayers as somewhat major antagonists: in the "age before ages", they discovered and woshipped an eldritch "nascent thought" known as Ilsensine, and in bringing knowledge of it back to the past set off a chain of events that caused the end of the world. While the mind flayer empires were overthrown and brought low, the gods of Law discovered Ilsensine and were consumed, followed by the other gods of the heavens (hence why Anachrononauts do not worship any and cannot make use of altars). In order to change the future and gain a full-scoring ascension, you must gain access to your Quest from your quest leader before she dies, retrieve the Annulus and obtain the Amulet of Yendor, then reach the lawful high altar on the Astral Plane and invoke the Annulus to purge Ilsensine's influence once and for all before ascending as normal.

Mind flayers are one of the many quest monsters: 17 of the randomly generated monsters are mind flayer-related - of those, 18 are mind flayers, 18 are master mind flayers, and the remaining monsters are either umber hulks or brain golems. Mind flayers are among the various H.P. Lovecraft-inspired r'lyehians that can appear as well, with a 17 chance of a r'lyehian generating: mind flayers make up 116 of randomly-generated r'lyehians. Many mind flayers are also generated scattered around the lower filler level(s) of the Quest at level creation. Genocide does not apply to monsters generated in the Quest branch, meaning that Anachrononauts cannot preemptively remove mind flayers to make their quest easier.


In xNetHack, mind flayers are moved to the aberration monster class, represented by U; this is done to avert the potential YASD for dwarven players using blessed scrolls of genocide, and also solves the problem of minesflayers.


In notdNetHack, in addition to dNetHack details, the Illithanachronounbinder is a role that acts as a playable mind flayer with the traits of whatever starting race you select in addition to those of mind flayers; the role's rank title for experience levels 14-17 is "Mind Flayer". notdNetHack also adds vilithids, vampiric mind flayers that are primarily seen on the Illithanachronounbinder quest.


In EvilHack, mind flayers and master mind flayers use h in order to differentiate them more easily for dwarven royals. EvilHack also adds alhoons (which are implemented differently from dNetHack) as well as mind flayer larva, which only generate within mind flayer nurseries. Mind flayer larva live in shallow pools and can only reach adulthood by attaching themselves to a victim's face; if a player is attacked this way, they have only one turn to kill or remove the larva before it burrows itself into the player's brain, killing them instantly and turning them into a mind flayer that can be found in any resulting bones.

Mind flayers are also a playable race, referred to as illithids; in addition to the above, other illithids can also be found in the dungeon as any of the various racial monsters present within, e.g. shopkeepers and player monsters. Player illithids have psychic resistance that renders them immune to brain-eating attacks, including those from other mind flayers.

Monster stats by variant

Mind flayer

Master mind flayer

Encyclopedia entry

This creature has a humanoid body, tentacles around its covered mouth, and three long fingers on each hand. Mind flayers are telepathic, and love to devour intelligent beings, especially humans. If they hit their victim with a tentacle, the mind flayer will slowly drain it of all intelligence, eventually killing its victim.