It’s a brain! With feet! What’s not to love? Well, the fact that it feeds on your consciousness and takes over your body, for one thing.

Old-school players of Advanced Dungeons & Dragons will remember the intellect devourer as one of the two most memorable monsters with psionics—that strange, complicated supplementary rule set that allowed for telepathy, telekinesis and neural combat. Fifth-edition D&D has dispensed with all that. Psionic power is now treated as either a special trait, a form of spellcasting or both. In the 5E intellect devourer, this is encapsulated in its telepathy and its Detect Sentience, Devour Intellect and Body Thief features.

According to the 5E Monster Manual  flavor text, intellect devourers are aberrations, created to serve the interests of mind flayers. They’re not independent creatures. You’re not going to randomly run into one in the woods. Rather, any intellect devourer your player characters encounter will be on some kind of mission. That will affect who it uses its powers on and when.

First, the usual breakdown. Intellect devourers have very low Strength alongside high Dexterity and Constitution, the profile of a skirmisher that relies on numbers. One doesn’t get the impression, however, that intellect devourers are a numerous species, so they’re not going to get many opportunities to overwhelm their opponents. They have slightly above-average Intelligence and average Wisdom and Charisma (by humanoid measure), so they’re not just animals—they can plan and adapt. They have proficiency in Stealth, and although they have no eyes or ears, they have 60 feet of blindsight and 300 feet of Detect Sentience.

Their Multiattack includes one use of the Devour Intellect power, and Devour Intellect may inflict the stunned condition or knock an opponent unconscious. Both of these conditions include incapacitation, and Body Thief requires an incapacitated humanoid opponent, so there’s how these features fit together: the intellect devourer uses Devour Intellect until it stuns an opponent, then uses Body Thief against it.

How long will it take for Devour Intellect to stun an opponent? That depends on the opponent’s Intelligence. Let’s look at three cases: an ordinary commoner, an average adventurer and an adventurer whose prime requisite ability is Intelligence and who has proficiency in Intelligence saving throws:

  • A commoner with Intelligence 10 has a 55 percent chance of failing his or her saving throw against Devour Intellect, whereupon the intellect devourer has about a 62 percent chance to stun. Chance of both happening: about 34 percent.
  • An average adventurer with Intelligence 12 has a 50 percent chance of failing his or her saving throw, and the chance to stun is about 37 percent. Chance of both happening: about 19 percent.
  • A low-level wizard with Intelligence 15 and a +2 proficiency modifier has a 35 percent chance of failing his or her save, and the chance to stun is only about 9 percent. Chance of both happening: about 3 percent.

Doesn’t look like any adventurers are getting their brains eaten today, does it? It takes two rounds for the devourer to have a better than 50 percent chance of stunning a commoner, three rounds to have a better than two-thirds chance. In contrast, three rounds aren’t enough to give the intellect devourer even a 50/50 chance of stunning the average adventurer, and the wizard can wait that brain-puppy out more than long enough for his associate, Hrodvald Thunderfist, to squash it.

This leads us to an interesting conclusion: When a party of PCs first encounters an intellect devourer, it probably won’t be in the form of an intellect devourer. Instead, it will be puppeting the body of a commoner whose intellect it’s already devoured. (By the way, there’s an error in the MM stat block. It’s not enough to reduce the host body to 0 hp in order to drive the intellect devourer out: the body must actually die, or one of the other two listed methods must be used.) The only PC an intellect devourer is ever likely to attack with Devour Intellect is one who’s chosen Intelligence as his or her dump stat.

Let’s pause for a moment and note that stunning and unconsciousness aren’t the only conditions that include incapacitation. A person who’s paralyzed or petrified is also incapacitated, so a humanoid in the grasp of a hold person spell, for example, would also be vulnerable to a Body Thief attack. And hypnotic pattern and Tasha’s hideous laughter are two low-level spells that can inflict incapacitation directly. An intellect devourer that had already taken over the body of a spellcaster who knew hypnotic pattern (an extraordinarily unlucky spellcaster, we’d have to conclude from the probabilities above) could easily use that spell to prepare host bodies for other intellect devourers without their having to Devour Intellect at all. (Sleep would work as well.) Note also that Body Thief doesn’t give the target immunity if the intellect devourer doesn’t succeed on its first try.

OK, so what’s an intellect devourer doing while it’s puppeting a host body? Whatever it’s been instructed to do, as unobtrusively as it can. The host body is only useful as long as the guise is maintained. An intellect devourer ejected from its host will run like a rat, fighting only if cornered. (In that situation, it uses its Multiattack, attacking with its claws and using Devour Intellect on its opponent, but it may or may not use Body Thief on an incapacitated opponent—it depends on whether that would help it make its getaway.) It’s resistant to damage from normal weapons, its armor class isn’t especially high, and it has a high movement speed, so a fleeing intellect devourer will Dash rather than Dodge. With one exception: On its first turn trying to escape, if it’s got two or more unsurprised melee attackers in adjacent squares or hexes, its first action will be to Disengage.

And what about that instance in which the brain-puppy tries Devour Intellect on a dimmer PC? It’s not going to do it out in the open, that’s for sure. It will use Stealth to hide in ambush, until the PC comes within 10 feet of it. It will use only Devour Intellect, not its claw/Devour Multiattack. This way, it doesn’t give its position away if it fails, because Devour Intellect technically is not an attack—Hrodvald simply has an unexplained splitting headache all of a sudden. If the intellect devourer can’t bring down its target in three rounds, it abandons the effort and scampers away. That will give its position away, but it should have little or no trouble escaping.

Next: mind flayers.

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