Especially Nasty – Intellect Devourer Delusion

This creature uses the curse rules as a foundation, taking them in a slightly different direction. There’s no moral lesson to this “curse”, just the unremitting terror of having your mind eroded, bite by bite. This is how intellect devourers are born.

In addition, there are a few elements which use the corruption rules. Simply ignore any mentions of corruption if you’re not using that subsystem.

Intellect Devourer Delusion

Transgression: You’ve really annoyed someone really unpleasant. Alternatively, this could be the side effect of severe corruption.

Associated Icons: Archmage, Lich King, Prince of Shadows, The Three, some horrorific fallen or rising icon.

When the curse strikes: All throughout the session, you feel like you’re being watched. As Germination (see below) rises, you’ll start hearing a voice, nonsensical at first, then issuing instructions or insults. At the beginning of combat during this session, you become aware of an intellect devourer hiding somewhere on the battlefield. It’ll keep reappearing this session until either Germination or Comprehension is increased.

Some Assembly Required

The nascent intellect devourer always matches the capabilities of its host. Find the “base stats for normal monsters” on page 254 of the core book and use them to replace all the ‘x’s in the write-up below. The intellect devourer’s level is equal to the level of the host, MD is its better defense, and Initiative is equal to its level +4. See below for the way the effective hp are calculated. If you’re feeling fancy, you may wish to further customize these numbers to better suit the infected PC. Take a look at the previous page for simple adjustments. For instance, if the host is a healer, you could make its intellect devourer a scrapper (+3 to attack, 70% of normal hp); or if the host is a “glass cannon”, the intellect devourer could be an oaf (-3 to attacks, +3 to AC).

Delusion Progress

There are two parameters that track the progress of the intellect devourer growing inside the poor host’s head: Comprehension and Germination, both starting at 1. Comprehension is a measure of success the host has in understanding and ultimately overcoming the intellect devourer. It goes up by 1 each time the character defeats the intellect devourer. Germination, on the other hand, measures how close the intellect devourer is to completely overtaking the host’s personality, growing legs, and attaining freedom. Germination goes up by 1 each time the intellect devourer knocks out the host with psychic damage at the end of the fight.

Comprehension affects the intellect devourer’s total hp: it has 50% of the hp it’s supposed to have according to the table when Comprehension is 1, 75% when Comprehension is 2, and 100% when Comprehension is 3. This may seem counterintuitive: the better the host understands the threat, the harder it is to vanquish. However, while their comprehension is 1 or 2, they cannot truly defeat it: it slinks away back into the recesses of their mind. Once Comprehension reaches 4, the intellect devourer is actually destroyed.

Germination makes it easier for the intellect devourer to use its abilities. In addition, whenever Germination goes up, have the player choose a background their character has. Now it belongs to the intellect devourer. But it’s fine, it’s willing to share. Every time the character uses the stolen background, they risk corruption, and the memories they draw upon are dissociated from their own point of view. Describe a mundance scene relating to the background, as observed by an alien intellect.

Due to the way the intellect devourer’s psychic damage is applied (see below), both Germination and Comprehension can go up simultaneously. Should both reach 4, the host is left in an unenviable position of being in total control of an intellect devourer that has hijacked their former body.

Nascent Intellect Devourer

“You are worthless. Just give up. Let me out. I’ll take care of everything.”

Initiative level +4

Host’s level spoiler [ABERRATION]

[Special trigger] C: Anxiety +x vs MD – the host rolls damage as if they’d hit themselves with the attack they used, dealing psychic damage.

Limited use: Use as an interrupt when the host attacks and an opportunity presents itself.

[Special trigger] C: Delusion + x vs MD – the condition against which the save was made is applied again, even if the save wasn’t successful, except any damage it deals is psychic. It’s not considered to be the same effect, though, e.g. if a creature gains a bonus to attacking those suffering ongoing fire damage, ongoing psychic damage of thinking you’re on fire won’t help it.

Limited use: Use as an interrupt when the host makes a save and an opportunity presents itself.

[Special trigger] C: Paranoia +x vs MD – the ally rolls damage as if they’d hit the host as well, dealing psychic damage.

Limited use: Use as an interrupt when the host’s ally attacks an enemy nearby the host, and an opportunity presents itself.

C: Your lying eyes (nearby host) + x vs MD – x psychic damage, and the intellect devourer teleports to a nearby location.

Limited use: Use only when the intellect devourer hadn’t used any interrupts abilities since the end of its previous turn.

Opportunist: Several of the intellect devourer’s abilities can be used “when an opportunity presents itself” while some specified action occurs. With Germination 1, the ability can be used when the action resulted in failure and the natural roll was odd. With Germination 2, the ability can be used when the natural roll was odd, no matter action’s success. Finally, with Germination 3 the ability can be used when the natural roll was odd and on any roll when the action resulted in failure. The host can risk corruption to deny the intellect devourer an opportunity.

Mind playing tricks: Only the character suffering from the delusion can see or in any way interact with the intellect devourer. It’s all in their head. Quite literally: they’re not being stalked by a montser, the monster is growing inside their brain.

Identity crisis: Keep track of the damage dealt by the intellect devourer separately – do not subtract it from your hit point total. You can’t heal it either. Instead, the damage applies all at once at the end of the fight.


This is as horrific as a monster gets. A parasite stealing one’s mind, a memory at a time. A disembodied voice critizicing every decision they make. An alien thing they share their head with. It is an opportunity for the GM to pull out all the stops, especially in the sessions when the “curse” strikes. Don’t let the few ideas mentioned so far limit you. Get under your player’s skin, inside their skull, and wriggle those growing legs. At the same time…

A word of caution

As you can see, the intellect devourer delusion is not just a nasty critter, but a not-so-subtle metaphor for mental illness. For some players, it may simply be a challenge to overcome. For others, it could potentially be catarthic to squash the embodiment of the horrible voice inside their head. Others still could be using games to escape similar real-world troubles. Just… be mindful.

Depending on your players, it may be a good idea to reframe the intellect devourer’s influence as insidiously helpful instead of anxiety-inducing. In that case, it wants to be your friend, a better friend than any of the fake friends you have. Anxiety becomes Earnest concern: “Oh no,” it says, “Look how clumsy you are. That’s ok, let me help.”

One thought on “Especially Nasty – Intellect Devourer Delusion

  1. I’m thinking of putting together a pdf of all the Especially Nasty monsters, published both here and in the Escalation fanzine, as well as the subsystems I wrote for 13th Age. Basically most things under the tag. I’d put it up as Pay What You Want on DriveThruRPG. Would you be interested in downloading such pdf?

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