5E Let's Read: Volo's Monsters

The ranks of the Fey continue to swell, as we turn to consider the Meenlock, a creature that is born of fear and exists to spread it.

The art in Volo’s is great, with the proportions and strange anatomy of the Meenlock fully on display. I like the left foot perched on a human skull as well - it’s the kind of macabre detail that suits the flavour text of these guys.

The Fey society must be a strange one, as significant numbers of the sub-species simply pop into being around strong emotion - in the case of Meenlocks, fear brings them and their lair into being. This entry is one that essentially presents a complete story seed to the DM: some act of great evil and fear brings a hive of Meenlocks into being. They then kidnap people, telepathically torture them, and convert them into more Meenlocks. The players come into the situation presumably after someone important has been kidnapped, meaning that they need to hustle to rescue them, before it is too late. The flavour text devotes most of its time to discussion of the Meenlocks’ telepathic abilities, their lair, and how they come into being; we don’t learn a huge amount about about their culture, perhaps because they don’t really have one beyond ‘cause fear’, despite them being essentially human in their statline.

The Meenlocks seem to be very strong contenders for an early-game horror experience. Their abilities are all focused around fear or darkness, and they actually get weaker in ‘bright light’, not just sunlight, so there is definitely potential for an Alan Wake / Doom 3 experience of using light to banish the darkness. They hide during the day, and only come out at night, as is appropriate for horror, and they are usually found in forests but can be found in underground and urban settings. The latter is a pretty interesting one, and I think that I’d really like to use some of these lurking underneath a magical university, preying on the students who study too late in the library.

The Meenlocks are reasonably weak creatures, whose solid statblock has good movement options (Shadow Teleport on a bonus action) and a single strong attack that does a paralyse for one minute, albeit on an easy save (since Constitution saves are generally favoured by everyone likely to be in the front line). However, as mentioned above, they have Light Sensitivity, which will make them a lot easier to fight once the players take advantage of that, depending on how generous you are with interpreting use of Light cantrips and the like. I think that this will allow you use to more of them than you might otherwise be able to: you can start with a single one, which is scary and powerful, and then have a climatic fight with several, when the players have learned and taken advantage of their weakness.


Possibly a Idiot.
Back in Chapter one, Meenlocks were listed a a "brute" ally of the Hags. Meaning that the Hag's employ them as mercenaries, but don't trust them to keep around as full time servants. Additionally, an Annis Hag with Regional Effects can set up a lair of these creatures. So, let's see where that can take us.

In a mixed group of of such mercenaries. The Meenlocks role becomes that of disrupting the back line. Using their Shadow Teleport, they can slip in behind all the warrior types and try to paralyze the squishy casters or skill-monkeys. Any warrior who pulls back to help is susceptible to their fear aura and may not be able to help in time. They pair up particularly well with Shadow Mastiffs and Yeth Hounds, due to all of them sharing a weakness to the light, and their multiple ways to cause fear in the party. Oni's, in particular, can set up areas of Darkness for them to exploit, while distracting the front-line with their bulk. And if the mercenary band has any skirmisher types darting around the battlefield, such as a Quickling, make sure they keep an eye out for any target the Meenlock has paralyzed. A few choice critical hits are a juicy opportunity for carnage and a great way to make the party consider running away.


Two things of potential interest.

Meenlocks are small in size, yet they can take any medium or large humanoid and turn them into meenlocks. To me, this gives us a beautiful visual set-up, where the players walk in on someone who is mid-way through the transformation and see a person literally shrunken and twisted by fear.

Jumping off that, they torture people who are incapacitated. Sleeping is being incapacitated. Pair these guys with someone like the Night Hag who can prevent a target from gaining the benefit of a long rest. How long does it take the former adventurer king, unable to sleep, tortured by horrific visions every night, to succumb when his body and mind are slowly being destroyed by this hag and her meenlocks. Bonus round, the hag obviously doesn't want his soul if the meenlocks get him, so who hired her to terrorize a kingdom in such a brutal manner.

The second thought I had, is that the Meenlocks "spontaneously arise" when someone is overcome with fear. Think failing a save against fear is enough? Fighting an enemy spellcaster or some other entity capable of inflicting fear, in a land near the Feywilds. The evil warlock casts a spell, the fighter falls back, scared witless. Suddenly the land cracks and twists, and these horrific chittering monstrosities come pouring out of the earth, eager to drag the party into the depths.

Instant allies, and any time you can change the very land the players stand on mid-combat, they are going to feel it and remember it.
The Meenlocks make me wonder what the fey world looks like for 5E. I've wondered it in the past, but they're really the ones who drop the hint that sections of it may be truly Lovecraftian in nature.

I would definitely use them to surprise a low-level group who hear there's a fey problem and expect pixies.
I hadn't thought about them in the context of allies to Hags, but you guys are right to say that there is real potential there. They can get a lost nastier if a Hag pre-casts Fog Cloud or something similar to obscure darkness, and their teleporting shenanigans lets them pop around the back ranks easily. I think that the Fey are a little tougher to get a grasp on, as a combat encounter, than the Gnolls are; for the latter it is easy to see how they work together, while the Fey have so many strange and divergent abilities that seem to combine oddly.
@Chaosmancer , that's a great plot idea for the king being tormented. As you say, it leads to the question of who is behind it - and you can use it as the lead into a whole Feywild themed adventure.

I might go and edit the contents list to show which creatures are Fey. They're hard to keep track of! Using Kobold.club, we get the following list of Fey in the game:

Boggle (CR 1/8) [VGtM 128]
Blink Dog (CR 1/4) [MM 318]
Pixie (CR 1/4) [MM 253]
Sprite (CR 1/4) [MM 283]
Darkling (CR 1/2) [VGtM 134]
Satyr (CR 1/2) [MM 267]
Dryad (CR 1) [MM 121]
Quickling (CR 1) [VGtM 187]
Darkling Elder (CR 2) [VGtM 134]
Meenlock (CR 2) [VGtM 170]
Sea Hag (CR 2) [MM 179]
Green Hag (CR 3) [MM 177]
Redcap (CR 3) [VGtM 188]
Warlock of the Archfey (CR 4) [VGtM 219] *
Yeth Hound (CR 4) [VGtM 201]
Annis Hag (CR 6) [VGtM 159]
Bheur Hag (CR 7) [VGtM 160]
Korred (CR 7) [VGtM 168]

So we've still got the Yeth Hound, Redcap, and Quickling to come in this series. The above list doesn't include the Banderhobb (CR 5) [VGtM 122], but that is because ol' Bandy is a Monstrosity. Other things you could happily include as relevant to Fey adventures would be Treants, various Giant Animals, Catoblepas, and the like.

* Okay, so this guy is actually humanoid (any race), but he might well work as a generic 'Fey spellcaster'.
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Right lads and ladies, we now come to the Illithid section of the book. I hope you’re not squeamish, because some of this stuff is pretty rank. We begin with the Alhoon. a renegade Illithid who turned away from its people - not out of a sense of outraged morality or to join the sunlit uplands of the surface world, but instead because it craved arcane power. They’re nasty customers, and have even more plot potential than normal Mind Flayers.

The image in the book relies heavily upon colour contrast, with the alabaster-pale skin of the Alhoon standing out starkly from the black and midnight-sky robes that it is wearing. Though Mind Flayers don’t really possess expressions, this one nonetheless gives an aura of mad malevolence with its staring eye.

So the Alhoons get one of the longest entries in the book, at two full pages, and the space is put to good use. They are renegades who seek out Arcane power, but are also driven by fear of the oblivion of death. As a result, they work together to create and protect special pseudo-phylacteries, and they also tend to search for the secret of lichdom with great vigour. There are a lot of meat on these plot-hook-bones; for starters, you have the fact that Alhoons work together, giving you the perfect excuse for the players to fight a whole series of them. If the players get hold of the pseudo-phylactery, then the wielder gets bonuses against them, which could be really cool; it makes me think of the end of Dark City when the protagonist unlocked his full potential.

On top of their semi-lichdom, these guys remain Mind Flayers, so you can still use them as Lovecraftian tentacle horror, and I think that using the usual range of minions (Intellect Devourers, thralls, Cranium Rats, etc) will be fine. Their relationship to the Mind Flayer hive is quite interesting, with them being outcasts but ones who still covet the companionship of the Elder Brain’s communion; some seek to take over a colony and replace the Elder Brain, which might make for a jolly interesting storyline if your campaign is in the underdark. The idea of players working with an Alhoon to stage a coup - in return for a promise of aid or protection for a local community from attacks - is one that really appeals.

One final comment that I’d have on these guys plot wise, is that you also have the fact that they are wizards, and will seek out knowledge. If your campaign features magic book shops, or even an arcane university, then an Alhoon disguised as a normal wizard might be a great plot twist. They do, after all, have Disguise Self

The statblock for the Alhoon is interesting, and basically combines the Mage with the Mind Flayer; level 6 spells, as a 12th level Wizard, on top of a Mind Flayer’s Psionics, Mind Blast and Magic Resistance; their undead status also gives them a Turn Resistance ability. The spells are solid combat ones that you will recognise from your party wizard’s repertoire, and features both defensive and offensive options. Their resistances, and especially spell resistance, will be an unpleasant surprise for anyone hoping to win a spell duel. I think that the best use of them will likely be to start with Mind Blast to weaken and slow the party, before then moving onto spellcasting; if you are cruel enough to use multiple at once, then opening with a barrage of Mind Blasts is going to be very effective against many groups, and perfectly sets up the Alhoons to then use powerful spells on the second turn against now-weakened opponents.

Finally, we get a lengthy sidebar that tells us how to turn a Lich into a Mind Flayer version, the Illithilich, including alternative Legendary Actions. Remember that this version combines immunity to low level spells with advantage on saving throws against all spells, and you will understand why it would be the absolute terror of any spellcasting community that it comes into contact with. Oddly, the Lich has more Mind Flayer abilities than the Alhoon - specifically, the ability to eat brains. I don’t want to make this post any longer than it already is, so I won’t discuss the Illithilich much - others are welcome to do so, however! - except to note that I think they are tough campaign ending bosses to use because of their combined tone; both Lich and Mind Flayer, it seems like they will be harder to theme a whole campaign around them then either a Lich or an Elder Brain individually would be.


Possibly a Idiot.
As a contrast to the Illithilich, the Monstrous Manual has a variant stat block for a Mind Flayer Arcanist: A CR 8 living Mind Flayer with the spellcasting power of a level 10 wizard. Using this example, you could easily glue some tentacles on to the various wizards found in the back of Volo's Guide. Just remember that their CR is going to be a minimum of 7 after such a modification.

I actually think it would be relatively easy to theme a campaign around an Illithilich, the hardest part being incorporating psionics into your world (the current UA leaves much to be desired, but they are working on it)

Let's start from the bottom Up: The Party finds out about the Gith.
The Gith can be introduced at a low tier of play, the Githyanki Warrior clocks in at CR3, making them ideal "first bosses". Where a Githzarai Monk pulls CR2. Both of them are Humanoids, allowing them to pilfer other humanoid stat blocks with ease.

Setting up the first arc, a Group of Githyanki come to the Prime in order to hunt down and kill some mind flayers, being the evil kin of the Gith, they don't give a damn about what gets in their way. Gith are known to be warriors, mages, and especially warrior-mages (the origin of the word "Gish") allowing many different kinds of encounters to be set up to feature them. They like to ride around on red dragons, salt the earth in their wake, all that kind of jazz. Good stuff for a t1-t2.

The Githzerai, on the other hand, also hate mindflayers, but don't go too far out of their way to find them. However, having heard that the Githyanki may have found a potential layer of them, they will investigate. Githzerai are Monks, and Mystics(psions), and Mystic-Monk/warriors who are called Zerth. Also potentially Clerics, but not often. They aren't all about the salting of the earth, and don't have red dragons to back them up, so they may be convinced to acquire aid from the PC's, if the PC's don't end up blindly attacking them due to the fact they look like the Githyanki.

At any rate, these two groups will naturally start to fight eachother, as they are inclined to, do to their religious upbringings. Causing a good many plot hooks until the PC's are powerful enough to actually fight the mindflayers minions themselves. Featuring all the aberrations that you know and love to hate in the underdark below whatever town the PC's happen to be housed out of.

I would also recommend using an Ulitharid as the leader of the Mind flayers instead of an Elder brain, they are significantly easier to fight, and also serve as a plausible reason as to why the Illithids were found out. They lack an experienced Elder Brain to lead them, and the snowball started rolling from there.

During this climatic fight is where the twist to the campaign comes in. The Mind flayers are routed, but not all of them, and not before killing off a Githyanki Mage (necromancer, possibly), securing her spellbook in the process of a grand three-way brawl. From here, the PC's think they have won the day, having stopped two threats at once, and go home to get some drinks or whatever.

In the meantime, the surviving Mind Flayers start dabbling in magic, because they have access to it now, and because their previous plan exploded so horribly in their squid-faces that anything else seems like it could be a good idea. After learning to cast spells, they start raiding wizard towers and schools across the land, using the combination of their abilities to great effect and amassing more arcane power. This second arc is short lived due to necessity. The PC's know what it looks like when a mind flayer flays a mind, so they will get into gear really quick. Expect some curb stomping, and for the PC's to become slightly more paranoid after the fact.

In the third arc, the we pull a bait and switch. Using a plot thread from from the Lich itself, we throw demons and cultists of Orcus at the party, letting an undead menace sweep out across the land. The PC's should take this at face value, because you just used mind flayers as a plot point twice, and Orcus is an end-game threat himself. The party gets on the trail, hunting down various undead, leading up to a Dracolich of some kind. Because Dracoliches are cool, and also serve as an experiment in lichdom. Once they confront the Dracolich, they learn who made such a horrible thing: The Alloons, who are quickly unlocking the secrets of true lichdom.

Now in arc 4, party must track down the mind flayers again, only this time with all kinds of the most twisted undead experiments imaginable blocking their path. Eventually, the party finds the way, only to find they were too late, and now have to fight an Illithilich.

Also, check out these sweet helmets on the Illithids, again from Dragon+. This is my second favorite look for them, right behind their Origami rendition.



One awesome thing about the Alhoon's "pseudo-phylactery" is that we have a ticking clock, unlike the Lich's Phylactery which is incredibly vague on how often you need to sacrifice souls to it.

The periapt of mind trapping only maintains the life of the Alhoon for the same number of years as the sacrifice had already lived, leeching the energy from them. This makes them very interested in hunting the long-lived races. An Alhoon really doesn't care so much about hunting humans, because at best they are get 80 years. An old Elf or Gnome will net them an additional 800 years or more.

So, how does an Alhoon track down, capture and sacrifice the oldest mortal creatures they could? Perhaps a community is living in terror, knowing that their elder is being targeted by a cabal of Alhoons, all jockeying to be the one who captures the elder and sacrifices them for long life.
So, how does an Alhoon track down, capture and sacrifice the oldest mortal creatures they could?
Get some minions that create a retirement home that specializes in longer-lived races. Let it run for awhile without culling any of the residents to build up a good reputation.

Then imagine the look on a player's face when they hear that "Pelor's House of Elderly Care" is actually an Alhoon's feeding ground.
The Elder Brain is the centre of Mind Flayer culture and hierarchy, and it is a surprisingly interesting antagonist for a giant organ sitting in brine.

I couldn’t resist posting some Baldur’s Gate love! I’m a big fan of the art in the book, as the Eldar Brain rises from water that is glowing pink, its tentacles looking armoured and dangerous. It gives the creature a real sense of menace, as opposed to its usual helpless victim visual.

The Elder Brain is vitally important to the Illithids, being both the leader of their colony and something akin to their god and guardian of their afterlife, so in general it is not something that the players are going to stumble across in a random dungeon room. This creature is meant to be the very pinnacle of the Mind Flayer dungeon, and it can track the thoughts of creatures from five miles out. They are essentially immobile, and it is usually impractical for the Mind Flayers to move one once it is fully grown and ensconced (they grow from Ulitharids, up next), so the Elder Brain is not going to flee your players; however, it is also likely to have the most stern defences possible.

There is some plot potential around the Elder Brain beyond just the final boss of a Mind Flayer dungeon. The first is its ability to dip into the minds of those within five miles. This means that if one is able to be near a humanoid settlement - either from a colony settling there, or the Mind Flayers managing to move it - then it can cause all kinds of chaos. There are a lot of monsters in D&D that can infiltrate or mind control members of a city; the Elder Brain is, let’s say, better than most. In addition, the Elder Brain needs brains to live; if all the Mind Flayers are dead - perhaps because the Brain managed to survive an attack that its minions did not - then it will be forced to use its mind control powers to draw food to it. This could be spun into a ghost-haunted dungeon, perhaps, with the players fighting various spectral undead before finding a half-starved Elder Brain, in what would be a good change of pace.

In combat, the Elder Brain is CR 14, and really underwhelming. It has terrible AC but loads of HP, which probably balances out. The real problem is that it has dreadful action economy and it is very likely that the players will fight it and take little or no damage. On its turns, the Elder Brain can do a single Mind Blast, or a single Tentacle attack, both of which do only slightly more than a single attack from a Giant. The Tentacle is basically a waste of time, unless you are wanting to go easy on the players, while the Mind Blast is critical to unlock any of the actually interesting elements of the Elder Brain’s abilities. Instead of making these attacks, the Elder Brain can use its action to do Psychic Link, which lets it read the mind of one creature and, using various Legendary Actions, do mildly nasty things to them - but it can only do that to an incapacitated opponent. So to get access to the psionic abilities that you want this creature for, you need to first use Mind Blast, hope that it stuns someone for long enough that on its next turn it can use Psychic Link - which does not require a saving throw - to then use Legendary Actions thereafter. By the time that you make this chain work, the combat will be over. It does sound terrifying though, so any players that have not read the statblock will likely be impressed by what is going on. However, the Elder Brain is actually going to do the most damage from random Tentacle attacks done as Legendary Actions, and I suspect that you’ll do better to challenge your players by just totally ignoring the Psychic Link stuff - leaving it to be the explanation for Thralls under its sway in humanoid settlements - and instead just use Tentacle legendary actions and Mind Blast actions to fill the combat with, which is really quite disappointing for a CR 14 master psionicist.

What do you guys think; am I being too harsh here? Am I, as usual, missing out on key synergies and interesting abilities?

Cap'n Kobold

How does its action economy look if you assume that the party will be fighting several Mind Flayers as well as the Elder Brain, rather than just the Elder Brain on its own?


The elder brain should always be surrounded by mind flayers.
The Elder Brain isn't really a combatant, it's more like a library that has indoctrinated a civilization of kleptomaniac book-thieves.


Unless I'm mistaken, the Elder Brain has Plane Shift (like all illithids) as a sort of escape option in case things go South, and I would expect it to shift out if it was clearly in danger.

As written, it's a fairly weak enemy for a group of mid to high evel adventurers and in some ways worse than a regular mind flayer which can at least leverage movement options in a fight. It relies almost completely on minions to protect it from dangerous foes.

As a visual, I recommend removing the tentacle and making its attack telekinetic in nature, maybe even dealing force damage.

Actually, one way to really spice it up might be to give the brain the options of having a permanently active Telekinesis spell (no concentration duration) and give it the options in the spell description in lieu of its tentacle attack legendary action.
Adding minions does change things, but you also then run into the rather embarrassing situation that the Elder Brain is basically going to look like a Mind Flayer with some out-of-sequence melee attacks. Is that what we were hoping for from the boss monster of this smartest of enemy races?

The main benefit of the Mind Flayer minions, I suppose, is that the Elder Brain can then trigger its Psychic Link off of their Mind Blasts. And you also end up with an astronomical EXP budget for the fight, when the players might not find it any tougher than just having another Mind Flayer in the mix.
In combat, the Elder Brain is CR 14, and really underwhelming.

That's my main issue here too. As an almost god-like being, it should have a CR closer to 20, with the abilities to match. It doesn't matter if it is surrounded by other mind flayers and so on - it should be a tough fight even after everything else in the settlement has been cleared. If I ever run one, I'll be homebrewing it to be somewhat tougher - CR 16 at the least, and maybe up as far as CR 19 - 20.

This is one of the two "boss" creatures in the book where I feel the CR was far too low.


Possibly a Idiot.
What do you guys think; am I being too harsh here? Am I, as usual, missing out on key synergies and interesting abilities?
Psychic Link has a range of 5 miles, thanks to Creature Sense. Also Sense Thoughts lets the Elder brain implant false ideas and emotions into a Psychic Linked targets head. Including the idea "Your head is alright now, and not being messed with in any way shape or form. That voice you hear is normal."

Which means the boss fight with the Elder brain starts when you wander into it's territory and get stunned by a Illithid, or paralyzed, or knocked unconscious. or turned into stone. There is quite a bit of wiggle room here. After this point, the Elder brain is messing with one or more of the party members constantly, while they wander about for what could be hours in it's territory. Perception may not be reality, your friend could be a foe, you might not actually like Ma Gannie's Famous Meat Pies. Heck, the PC's don't even need to be the target of the ability. A familiar, or pet, or hireling could be the target that starts the domino chain.

Perhaps the PC's have an ally that suddenly sends out a Psychic pulse, damaging the party. What will the PC's do when they are suddenly being ambushed by something that could be a Mindflayer in Disguise? How will they feel when they find out they killed their friend and they weren't a mind flayer?
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In addition to Leatherheads excellent thoughts there is one more thing that should be considered.

Elder Brains don't move, which means they are always in their lair.

Their lair actions are:

-Elder Brain casts Wall of Force
-A 120 ft flash of inspiration that gives the target advantage on their next attack, saving throw, or ability check
-A 120 ft lockdown that prevents the being targeted from moving from their space if they fail the save.

Now, the big question is "How big is the Lair", is the Lair the multi-leveled, multi-sectional cathedral the Illithid have placed it in. If it is, then every combat, at count 20, the Elder Brain is affecting the players and the fight.

The biggest thing is the first lair action, Wall of Force. Immune to Damage, Immune to Magic, Immune to being dispelled, and concentration of 10 minutes. The only way through I can see immediately is casting Disintegrate. These means that it is completely possible for your party to be caught in an impossible situation. Unable to reach the brain, they would have to retreat to 70 ft away, while the Brain summons allies to deal with the intruders.

Also, being able to psychic link with any 10 creatures in a 5 mile radius, while you are going through a colony of Illithid Mind Blasting you constantly. At least a few members of the party will probably be psychic links by the time you actually reach this thing, and it will then just use them to kill you, while it is unreachable.

And, if everything goes south, and it is going to be destroyed, it just up and plane shifts away. A massively intelligent creature, with the ability to create powerful mind slaves, who now really wants you dead, hurting, and probably knows all your deep dark secrets.

If the players can reach and hit it, the Elder Brain isn't going to last long. But if it starts working on them as soon as they are within even 2 miles of it, and it makes use of Wall of Force to divide them in combats and protect itself... It is going to be a massive challenge for any party I think, unless they are well-informed and well-prepared.


That's my main issue here too. As an almost god-like being, it should have a CR closer to 20, with the abilities to match. It doesn't matter if it is surrounded by other mind flayers and so on - it should be a tough fight even after everything else in the settlement has been cleared. If I ever run one, I'll be homebrewing it to be somewhat tougher - CR 16 at the least, and maybe up as far as CR 19 - 20.

This is one of the two "boss" creatures in the book where I feel the CR was far too low.
Indeed. My plan is to wait and see what we get in terms of a close-to-final draft psion telepath, and just slam all of the abilities of the level 20 class onto it. On top of everything it already has. And also probably more HD. And, of course, nasty advantage taking of its psychic link ability. It's like 3.5 Mindsight on steroids.
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It just seems to me that all of these ideas make the Mind Flayer colony interesting to attack, but do nothing to make the Elder Brain itself a fun encounter. Let's take a look at the next entry!


The Ulitharid is a fairly simple creature at its root, a boss encounter version of the Mind Flayer. It is a little more complicated than its lesser brethren, but overall is essentially an upgrade, not a whole new creature.

The book image is interestingly detailed, but doesn’t betray the sheer size of the Ulitharid (at Large), and it is considerably more gangly looking than its normal kin from the Monster Manual art. In fact, the art for the Mind Flayer is really the problem with this Ulitharid art - the Monster Manual image is just so much more interesting and imposing.

Occasionally a tadpole will turn, not into a Mind Flayer, but into an Ulitharid. This results in some changes which seem to be mostly based on bee ecology, as now the colony will have two leaders: the Elder Brain, and the Ulitharid, which is an Elder-Brain-in-waiting. We are told that the relationship between the two can run the whole range between co-operative to hostile, which gives you a lot of flexibility in how you use an Ulitharid. For example, your players could arrive in the colony to find it ruinous, with the survivors of the two factions still fighting amongst the rubble. Alternatively, the Ulitharid could be the right-hand-flayer of the Elder Brain, giving you a mid-story boss monster that is more mobile than its master, yet shares many of its traits.

The staff carried by the Ulitharid is pretty cool; made of black metal (just like the staff from Terry Pratchett’s Sorcery), it has the ultimate function of allowing the Ulitharid’s transformation into an Elder Brain. The text here does not mention where the staff comes from, but presumably it takes crafting and a lot of effort by the colony; an Ulitharid that is trying to retrieve its staff might be another plot option, with a series of museum curators and private collectors suffering strokes as it tracks down its lost item.

The Ulitharid is basically a slightly tougher Mind Flayer, with a couple of the Elder Brain telepathy options added on. Its innate spellcasting is more robust, with Mass Suggestion and Feeblemind particularly catching my eye; the new spells give it some nasty options, especially when you realise how nasty the combination of Feeblemind (become int 1) and Mind Blast (make int save or be stunned) is. That combination used on the party Fighter or Barbarian might well take the character in question out of the fight for good. The Ulitharid also gets a couple spells that help with a leadership role - Scrying, Project Image - which combine with the Creature Sense and Psionic Hub to demonstrate how it could manipulate humanoids and other Mind Flayers into doing its will.

The combat options of the Ulitharid are basically just the same as those for the Mind Flayer, albeit with a slight boost in damage, to hit rolls, and save DCs as befits the increased CR. It is worth noting that the Ulitharid, like the Mind Flayer, is not the most robust of opponents - I used a pair of Mind Flayers last week, and was surprised at how quickly they fell once the players focused on them - so you may want to add something like a pair of thrall-Ogres as meatshields, if you plan for the fight to last a while. In other words, the Illithids are a bit of a glass cannon race, so prepare the combats accordingly.

I’m much more impressed with the Ulitharid than I am with the Elder Brain. Despite it being much lower CR than its master, the Ulitharid just seems a much more interesting combatant, and one that can radically change how a combat goes, using its increased psionic might. In addition, it has more story potential attached to it, though to be fair the Elder Brain is going to be intrinsically attached to any Mind Flayer storyline that you devise, rather than being a free agent, so that point is a bit unfair. Regardless, I feel that the Elder Brain is just part of a dungeon design - the last room, the explanation for why the players are under constant psionic attack - whereas the Ulitharid feels like a monster that can drive plots by itself.

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For the Feast ability, one easy way to try and get that opened up is if the hag attacks while the party is escorting or rescuing NPCs. The hag is mobile enough to get past the front-line, and they could hit the people the party is protecting.
It's also useful against parties who like hirelings and minions. (Conjured minions unfortunately vanish when reduced to zero HP, so it doesn't work there, but it would work against a Beastmaster's pet IIRC unless there is a humanoid-only restriction. AFB.)