“Mind flayers aren’t the real boss monster,” I wrote in my post on mind flayer tactics. “They usually live in colonies, not by themselves. The real boss monster is the elder brain.” And while the fifth-edition Monster Manual doesn’t include stats for elder brains, Volo’s Guide to Monsters does! Huzzah!
Unfortunately, Volo’s doesn’t solve the real problem with 5E mind flayers: that, as written, they simply aren’t powerful enough to carry out their psionic schemes with even a modicum of efficiency. And efficiency is important, because if they have to live near humanoid settlements in order to harvest the brains they live on, yet also have to conceal their presence in order to avoid discovery not just by their prey but also by vengeful gith, they’re gonna need a decent number of minions.
Volo’s chapter on mind flayer lore includes a nod to this:
A colony that desperately needs to increase its population concentrates on capturing humanoids to turn them into thralls and illithids. Operating individually or in small groups, its members use stealth and deception to infiltrate the humanoid community while keeping their presence secret. Lacking the numbers or the ability to overwhelm and dominate the entire population, a colony turns its research toward more effective ways to exert control, such as finding a way to amplify an elder brain’s power to enable it to exert influence over a greater distance.
This is smart; the trouble is, even the stat blocks in Volo’s don’t fully reflect it. It’s the “more effective ways to exert control” that are both badly needed and missing from both the 5E MM and Volo’s. In my treatment of mind flayers, I proposed three alternatives to the mind flayer’s dominate monster ability that might provide the necessary amplification of its psionic powers: Charm (as exemplified by the vampire), Enslave (as exemplified by the aboleth) and geas (either in its normal, ritual form or in an accelerated, single-action form). Any of these would also work for an elder brain, which also, inexplicably, has no method of mind control except the dominate monster spell.
“The process of transforming a creature into a thrall requires the entire colony’s energy and attention,” Volo’s contends. That’s . . . unsatisfying. More to the point, it’s unthreatening. To serve as proper villains, mind flayers need to be able to pull off an Invasion of the Body Snatchers–grade takeover. At a minimum, I think, a single mind flayer ought to be able to take temporary control of a single humanoid nearly effortlessly, and permanent control with some effort; a whole mind flayer colony should have no trouble bringing an entire village under its sway.
Back to the elder brain. This is a boss monster, complete with lair actions and regional effects. One of these regional effects is important enough to underline: “The elder brain can overhear any telepathic conversation happening within 5 miles of it.” Most player characters are content to converse using their mouthparts, but if you do have PCs who communicate telepathically, for whatever reason, their doing so tips off an elder brain to their intentions. (It’s aware of their presence no matter what, thanks to its Creature Sense feature, unless they’re using magic to conceal their minds. Invisibility, even greater invisibility, doesn’t cut it, nor does pass without trace.)
An elder brain is mobile, but barely so: it can move 5 feet per round on land, 10 feet per round in its pool. Anything with legs can outpace it. But that’s OK, because mobility is wholly unimportant to its combat tactics, for three reasons:
- Its Dexterity is merely average, whereas its Strength is high, and its Constitution is extraordinary. It’s a tank.
- Its tentacles have a 30-foot reach, and they can grapple.
- Its physical combat abilities matter only because its devastating Mind Blast attack has to recharge between uses. Its Constitution is extraordinary, but so are all its mental abilities. If it had the choice, it would use Mind Blast all the time.
It can also hover, by casting levitate; this costs an action, however, so there’s not much benefit to it.
Legendary Resistance gives the elder brain free successes on three failed saving throws per day. Other creatures that have this feature have such spectacular saving throw modifiers already, they may as well use it every time they fail a saving throw. For an elder brain, it’s a little different, because it has a conspicuous weakness: Dexterity. Against DC 13, an elder brain has an 85 percent chance of making a Wisdom save (98 percent against spells and other magical effects, thanks to Magic Resistance) and a 65 percent chance of making a Constitution save (88 percent against magic), but its chance of making a Dex save is only 40 percent (64 percent against magic). Also, boss battles tend to run longer than other battles, meaning the fight probably won’t be over after three rounds. Therefore, an elder brain will marshal its uses of Legendary Resistance to ensure that it has them whenever it needs to make a Dex save, forgoing the use of this feature the first time it fails a Con save (first and second times, if the effects are nonmagical), or if it ever fails a Wisdom save.
Psychic Link is a long-distance opportunity attack, used not during combat with the elder brain itself but in earlier combat encounters with minions of the elder brain. It targets “one incapacitated creature,” but reading between the lines, this includes any creature that’s paralyzed, petrified, stunned or unconscious—and Mind Blast stuns enemies. In addition, Psychic Link reaches as far as the elder brain’s Creature Sense, i.e., 5 miles.
Creature Sense can’t tell the elder brain when a creature is incapacitated. But Telepathic Hub can, if the elder brain is conversing telepathically with the mind flayer that the foe is in combat with, or any other that’s on the scene. The elder brain has to be the one to initiate this conversation, so decide in advance which of the elder brain’s minions within that 5-mile radius are serving as its security cameras. Incidentally, as far as I can tell, an elder brain can maintain up to 10 conversations through Telepathic Hub plus up to 10 Psychic Links, so there’s no need to be parsimonious.
The target of a Psychic Link is aware of it as soon as he or she regains the ability to act, but the elder brain can use Sense Thoughts to brainwash the target into feeling chill about it, at least for up to an hour. How’s that for a dirty trick?
In face-to-cerebrum combat, however, the elder brain has three choices: Mind Blast, a tentacle attack and whatever mind-controlling ability you’ve decided to give it (dominate monster being the default). It’s not even a choice, really: the elder brain always uses Mind Blast unless that ability is on recharge, and unlike the mind flayer’s Mind Blast, the elder brain’s Mind Blast has a circular rather than conical area of effect, nailing every creature of the elder brain’s choice within a 60-foot radius.
A hit from one of the elder brain’s tentacles grapples, but it doesn’t restrain, so it doesn’t get advantage on attacks against its grappled foes. It does, however, inflict an automatic 1d8 + 5 psychic damage against each grappled foe at the start of his or her turn.
The bludgeoning damage that the elder brain’s tentacle inflicts is greater than most PCs can dish out in a round, so it will usually favor this attack over taking control of an opponent’s mind. But like mind flayers, elder brains are most vulnerable to ranged weapon attacks, and an archer or crossbowman who can deal out more than 20 hp of damage in an average round (e.g., a ranger with Colossus Slayer plus an Extra Attack) is a ripe target for takeover. Not only does the proxy do more damage than the elder brain could do with one of its own tentacles, it also does so on its own turn, adding to the elder brain’s action economy.
Speaking of action economy, the elder brain has four legendary actions to choose from, plus its lair actions, which take place on initiative count 20. Three of the elder brain’s four legendary actions require it to have an active Psychic Link: Break Concentration disrupts concentration on a sustained spell and deals a small amount of psychic damage in the process. Psychic Pulse uses the target as a relay for the psionic equivalent of an electromagnetic pulse blast with a radius of 10 feet. Sever Psychic Link gives up the connection to the target but disorients the target in the process. The fourth, Tentacle, is a simple attack.
Psychic Pulse is a good choice if the linked target is within 10 feet of at least two other enemies of the elder brain. Break Concentration is the natural choice anytime the linked target casts a sustained spell that harms or weakens the elder brain and/or its allies, or buffs the target and/or his or her own allies. Sever Psychic Link is a funny one, precisely because it gives up the condition that allows it to be used in the first place. Use it against targets that the elder brain has decided it’s done with—because they’re keeping their distance from their allies, aren’t casting spells, and no longer need to be brainwashed to feel or believe anything.
Like certain other legendary creatures, an elder brain can’t use any of its lair actions two turns in a row. Casting wall of force is a juicy one, because once it’s cast, the elder brain can sustain it without having to use any further action, including lair actions, and keep it going for up to 10 rounds. It’s got to have a good reason to cast it, though. Blocking off escape is one. Projecting a protective dome over itself is another, although while this lets the elder brain use Mind Blast against creatures outside the dome, it can’t attack creatures outside with its tentacles. (But it can trap already grappled enemies inside the dome with it!) Subsequent uses of this lair action negate previous ones, because the elder brain can’t sustain two wall of force spells simultaneously.
The “freeze!” lair action is a good way to preempt a threatening enemy from charging, and the elder brain will use it against the opponent who seems most likely to do so. The ally-inspiring action is a good way to make sure that the most critical moments of the battle go the elder brain’s way.
Casting plane shift on itself is a good way for the elder brain to save itself if it’s badly wounded, but it can’t survive long outside its brine pool, and elder brains don’t share. If it’s going to plane shift out of its lair, it has to have another one to go to. If it doesn’t have one, it may have no choice but to fight to the death. If it does, it will vacate the premises when it’s seriously injured (reduced to 84 hp or fewer). Its self-preservation instinct is powerful, but so is its narcissism—it takes that much damage to convince the elder brain that these meat puppets could actually beat it.
The mind flayer minions of an elder brain will fight differently in its defense than they will in their own. As components in the colony’s hive mind, they place the survival of the colony—and, by extension, the elder brain—ahead of their own. Thus, rather than flee when moderately or seriously wounded, they’ll fight to the death in defense of their elder brain, and they’ll run interference for the elder brain the same way they’d normally have their own minions run interference for them. (Of course, non-illithid minions serve this purpose even better, so they’ll be the first line of defense; the mind flayers themselves will be the last.)