5E: Converting Monsters from White Dwarf Magazine for Fifth Edition


grammar " (one who died less than 30 minutes ago)" --> "(one who died less than 30 minutes previously)"

Can go either way on the CHA score increasing. Leaning to "yes"

Otherwise I think this is detailed enough to work. Might have to playtest it...

I'll update the the Brain-Eating above.

The previous version was:

Revising the Gu'en-Deeko brain eating…

Brain-Eating. If the gu'en-deeko spends 10 (2d3 + 6) minutes* eating the brain of a freshly killed humanoid (one who died less than 30 minutes ago), it gains the memories and many of the abilities of that humanoid one hour later. A gu'en-deeko can absorb skills, knowledge-based racial abilities such as Dwarven Combat Training, languages and most class abilities from the brain, but does not gain any physical traits or racial abilities of the humanoid whose brain it ate such as Ability Score increases, Darkvision, or Dwarven Resilience.
 *If it matters, the exact number of rounds it takes the gu'en-deeko to crack open a dead humanoid's skull and devour the brain can be determined by rolling 3d12 + 1d8 + 76.
 If a gu'en-deeko absorbs the brain of a humanoid with a level 3 or lower and a Challenge Rating of 1 or less [?], the skills, racial abilities, traits and class abilities it absorbed from the brain last for 1 year. The gu'en-deeko retains the brain's memories after the year ends, but none of the powers it gained.
 If a gu'en-deeko eats the brain of a humanoid with a level of 4 or higher or a Challenge Rating of 2 or more [?], the powers it gains last until it eats the brain of another humanoid whose level or Challenge Rating is the same or higher. If that happens, the gu'en-deeko gains the powers of the new brain and those powers it gained from the previous high-level brain are reduced to a 3rd-level character of that class, then vanish a year later (as above).
 If a gu'en-deeko eats the brain of a humanoid with a level of 6 or higher, a Challenge Rating of 3 or more, or a mental ability (INT, WIS, CHA) of 16 or higher [?], the gu'en-deeko must succeed at a Wisdom saving throw against a DC equal to 10 plus the Proficiency Bonus and highest Mental Ability Bonus of the humanoid the brain came from or go insane, believing itself to be the humanoid whose brain it devoured.
 [A gu'en-deeko's Charisma score increases to match the highest mental ability score from the brains it has eaten. If a gu'en-deeko acquires the class feature Ability Score Improvement from a stolen brain, it always invests the improvement in a physical ability score (STR, DEX, CON) rather than a mental one, regardless of how the humanoid it stole it from invested that class feature.].
 Powers gained via brain-eating never stack; if the gu'en-deeko gains the same ability multiple times, only the most powerful one applies. For example, if a gu'en-deeko ate the brains of a 2nd-level cleric, a 3rd-level bard, and a 3rd-level druid, it gains 3rd-level Spellcasting, not three separate sets of Spellcasting (see below for Gu'en-Deeko Spellcasting). A gu'en-deeko can possess multiple abilities that use spells if they are different types of magic-use. For example, it could possess Innate Spellcasting from multiple sources, such as a Drow Elf and a Svirfneblin, together with Spellcasting from a Wizard and Pact Magic from a Warlock, all at the same time. A gu'en-deeko is unable to gain class features granted by an external power without that power's permission. Thus, if a gu'en-deeko ate the brain of a warlock, the gu'en-deeko would have to strike a bargain with that warlock's otherworldly Patron to gain most of the warlock class abilities.
 If the gained power is controlled by a mental ability (INT, WIS, CHA), it uses the numerical modifiers of the humanoid it was stolen from rather than the gu'en-deeko's. A gu'en-deeko that eats the brain of a druid with Nature +6 will gain Nature +6, not the Nature +1 it would have from its own Intelligence score and Proficiency Bonus.
 If the gained power is controlled by a physical ability (STR, DEX, CON), the gu'en-deeko can use its own ability score bonuses if this would give it a better numerical modifier than the humanoid it was stolen from.
Increased Hit Points: The gu'en-deeko gains bonus hit points from brain-eating. [Rules for amount of bonus HP and increase to Hit Dice. [?]
Challenge Rating: [Guidance for the CR of a powerful gu'en-deeko. I'm thinking Challenge equals its base value or the CR of the most powerful humanoid whose brain powers it possesses. [?]
Spellcasting: ???.

It still needs some specifics of the Spellcasting to work out but we're almost there.

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you mean like which attribute to use?

No, more about how it uses & retains spells. I was thinking:

Spellcasting: If the gu'en-deeko eats one or more brains with the Spellcasting power, it uses the highest spellcasting level, spell save DC, to hit with spell attacks and number of spell slots among the brains it has eaten. A gu'en-deeko with Spellcasting cannot change the spells it has prepared like a cleric or wizard, but can only cast the spells the humanoid spellcasters whose brains it ate had prepared at the moment of their deaths. If a gu'en-deeko loses access to a brain's Spellcasting power, all prepared spells from that brain become one-use, fading from the gu'en-deeko's prepared spells list as soon as it casts them. If losing a brain's Spellcasting power causes a gu'en-deeko's number of spell slots to fall, the gu'en-deeko does not lose the spell slots immediately, but its surplus spell slots become one-use and are lost once they're used to cast a spell. If this causes the gu'en-deeko to lose all ability to cast spells of a given level, it also loses all prepared spells of that level.


That seems ok....?

Updating the Gu'en-Deeko.

I forgot to include "Its spellcasting ability is Charisma" in the Brain-Eating, it's added to the Working Draft.

It comes out to Challenge 2, which seems a bit feeble but it is for the "base version" and ones that have eaten a few brains should be more powerful.

Did we decide on whether to give them Stealth +3 or not? I'm inclined to leave that out. It can always get Stealth proficiencies from stolen brains.

Once that question is answered, the basic gu'en-deeko is finished apart from the Description.

I was planning on statting up a couple of examples, a Gu'en-Deeko Mage with similar brain powers as Thaaak and some kind of warrior type.

For the "Thaaak", I was thinking we should give it the brains of an NPC Spy, a Dwarf and the Spellcasting of either a 6th-level Wizard or an NPC Mage or Battlemage.

Giving it the rogue abilities of a Spy instead of a 2nd-level rogue like the AD&D original is a slight upgrade in power, but a 2nd-level Rogue's abilities are a bit weak.

I'd lean towards 6th-level wizard to retain the spell selection Thaaak had in The Halls of Tizun Thane.

I'd suggest giving him CHA 17 for nine spells and have a spell list with the eight spells the original Thaaak possessed plus blur to replace the cloak of displacement the original monster had.

We'll need to decide what Arcane Tradition Tizun Thane followed. I'm thinking maybe School of Enchantment? That'd give him the Hypnotic Gaze and Instinctive Charm powers as well as the base wizard's Arcane Recovery.

Oh, and this Gu'en-Deeko Wizard will have one Ability Score Improvement which I'd put in CON for 18 (+4), which makes its Hit Points 57 (6d8 + 24 plus 6 bonus hit points from Brain-Eating) or 12 more than a base gu'en-deeko, just like the original Thaaak who had Hit Dice 5D8+12 to the base 5D8.

I'd eyeball that as being Challenge 4.


I'm thinking it needs some kind of cap to Brain-Eating so the number of powers can't get too overboard. How about changing the level 3 or lower brains section to the following:

 If a gu'en-deeko absorbs the brain of a humanoid with a level 3 or lower and a Challenge Rating of 1 or less, the skills, racial abilities, traits and class abilities it absorbed from this low-powered brain last for 1 year. The gu'en-deeko retains the brain's memories after the year ends, but none of the powers it gained. A gu'en-deeko can possess the powers of up to five low-powered brains, if it eats a sixth the new brain replace the oldest of the low-powered brains in the gu'en-deeko's repertoire.


Gu'en-Deeko Mage
Medium monstrosity, chaotic neutral
Armor Class 15 (natural armor)
Hit Points 57 (6d8 + 24 plus 6 from Brain-Eating)
Speed 30 ft., climb 30 ft.

18 (+4)​
13 (+1)​
18 (+4)​
8 (–1)​
12 (+1)​
16 (+3)​

Saving Throws INT +1, WIS +3
Skills Arcana +5, Athletics +6, Deception +5, History +5, Insight +4, Investigation +5, Perception +6, Persuasion +5, Sleight of Hand +3, Stealth +3
Senses passive Perception 16
Languages Common, Dwarven, Elven (all from Brain-Eating)
Challenge 4 (1,100 XP) Proficiency Bonus +2

Brain-Eating. The gu'en-deeko mage has used its Brain-Eating power (see the base Gu'en-Deeko for details) and currently possesses the brain powers of a 6th-level human Wizard of the Enchantment School as well as those of a Dwarf Commoner and a Spy (see Appendix B: Nonplayer Characters in the Monster Manual, pages 344 and 349).

Cunning Action. On each of its turns, the gu'en-deeko mage can use a bonus action to take the Dash, Disengage, or Hide action.

Dwarf Traits. The gu'en-deeko mage possesses Dwarven Combat Training, Tool Proficiency in mason's tools and Stonecunning.

Spellcasting. The gu'en-deeko mage is a 6th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 13, +5 to hit with spell attacks). The mage has the following wizard spells prepared:
  • Cantrips (at will): fire bolt, light, mage hand, prestidigitation
  • 1st level (4 slots): charm person, sleep, shield, protection from evil and good
  • 2nd level (3 slots): blur, mirror image, hold person
  • 3rd level (3 slots): fireball, major image
Sneak Attack (1/turn). The gu'en-deeko mage deals an extra 7 (2d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the spy that isn't incapacitated and the spy doesn't have disadvantage on the attack roll.


Multiattack. The gu'en-deeko makes two fist attacks.

Fist. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) bludgeoning damage.

Hypnotic Gaze. As an action, the gu'en-deeko mage can choose one creature that it can see within 5 feet. If the target can see or hear the gu'en-deeko, it must succeed on a DC 13 Wisdom saving throw or be charmed until the end of the gu'en-deeko's next turn. The charmed creature's speed drops to 0, and the creature is incapacitated and visibly dazed.
 On subsequent turns, the gu'en-deeko can use its action to maintain this effect, extending its duration until the end of its next turn. However, the effect ends if it moves more than 5 feet away from the creature, if the creature can neither see nor hear it, or if the creature takes damage.
 Once the effect ends, or if the creature succeeds on its initial saving throw against this effect, the gu'en-deeko can't use Hypnotic Gaze on that creature again until it finishes a long rest.


Instinctive Charm. When a creature the gu'en-deeko mage can see within 30 feet of it makes an attack roll against the gu'en-deeko, it can use its reaction to divert the attack, provided that another creature is within the attack's range. The attacker must make a DC 13 Wisdom saving throw. On a failed save, the attacker must target the creature that is closest to the gu'en-deeko, not including you or itself. If multiple creatures are closest, the attacker chooses which one to target.
 On a successful save, the gu'en-deeko can't use this feature on the attacker again until it finishes a long rest.
 The gu'en-deeko mage must choose to use Instinctive Charm before knowing whether the attack hits or misses. Creatures that can't be charmed are immune to this effect.


This gu'en-deeko was once the servant of a wizard but was tricked into thinking its master plotted its destruction (it ate the brain of an assassin who had been told the wizard wanted to rid himself of his pet). After killing its master and eating his brain, the shock of discovering the truth and the powerful personality of its dead owner drove the gu'en-deeko completely insane and it started dressing and acting like the wizard, believing itself to be that nobleman.

(Originally appeared in White Dwarf Magazine #18 (Apr/May 1980) as part of "The Halls of Tizun Thane" by Albie Fiore.)
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So any preferences for the Martial Gu-en-Deeko I plan to stat up?

NPC options are Bandit Captain, Berserker, Gladiator, Knight and Veteran.

I like Gladiator (for the combat ability) with a side-order of Knight (for the personality and Leadership) plus one other humanoid brain.

How about we mix it up and make the third brain a monster of some kind, like a goblin, orc or lizardman.

Let's see, the Monster Manual humanoids are:
  1. Aarakocra (the mental image of it trying to use Dive Attack is hilarious)
  2. Bugbear (will give it Surprise Attack)
  3. Bullywug (grants Speak with Frogs and Toads)
  4. Duergar (gifts Enlarge and Invisibility, both very useful)
  5. Drow (provides Innate Spellcasting and maybe Fey Ancestry?)
  6. Githyanki (only Innate Spellcasting)
  7. Gnoll (its Rampage is useless as the gu'en-deeko has no bite attack)
  8. Gnome (Svirfneblin) (Gnome Cunning and Innate Spellcasting are OK)
  9. Goblin (its Nimble Escape is useful but situational)
  10. Grimlock (none of its traits are brain-based)
  11. Half-Dragon (I doubt its Fire Breath is brain-based)
  12. Hobgoblin (getting Martial Advantage isn't bad, but requires an ally)
  13. Jackalwere (this is surprising! It gets Pack Tactics, Shapechanger and Sleep Gaze as they're humanoid. I was sure this monster would be a monstrosity)
  14. Kenku (grants Ambusher and Mimicry)
  15. Kobold (only Pack Tactics)
  16. Kuo-Toa (I guess Otherworldly Perception and proficiency in Net, or add Spellcasting and Pincer Staff it it's a Whip?)
  17. Lizardfolk (nothing)
  18. Lycanthropes (all are too high CR to become side-brains)
  19. Merfolk (nothing)
  20. Orc (only Aggressive)
  21. Quaggoth (its Wounded Fury isn't much use)
  22. Sahuagin (now Blood Frenzy is very useful to a Berserker, plus it gets Shark Telepathy)
  23. Thri-Kreen (none of its traits come from the brain)
  24. Troglodyte (again, none of its traits are brain-based)
  25. Yuan-Ti Pureblood (ooh! Innate Spellcasting and Magic Resistance, both very nice)
Some of those abilities are very tempting. So tempting I'm tempted to make it two humanoid monster brains for a total of four brains.

Maybe we should determine the final brain(s) randomly? A range of 1 to 25 can be generated by rolling a d100 and dividing the result by four.

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