Errour, a monster

Edmund Spenser’s The Faerie Queene, considered by some to be “the first major work of fantasy in the Western world,” is an unfinished epic poem first published in 1590. It’s mostly a long — some might say interminably so — allegory exploring various forms of virtue by recounting the adventures of various questing knights. It also contains a pretty kick-ass monster against whom the Redcrosse knight faces off right at the outset: Errour.

Henry Ford's illustration of the Redcrosse knight and Errour
from Andrew Lang's The Red Romance Book (1921)

      Errour is half woman, half snake; for Spenser, she is an allegory for doctrinal error and falsehood. In game terms, Errour is a dream encounter a referee may use to challenge the taken-for-granted or unexamined beliefs of any character. This has obvious applications with regard to clerics and paladins, but could serve equally well against an atheistical thief, wizard, or fighter. Whenever a PC is acting like they have it all figured out (or even just when you're sick of their smug assuredness), let them meet Errour.

Errour

Detail from Cynthia Sheppard's cover to the Grindhouse
edition of Lamentations of the Flame Princess (2011)

Errour appears when the target PC — the smug one — sleeps. The PC awakens to see a dark, cavernous hole that has inexplicably appeared nearby. (The referee is advised not to inform the players that this is taking place in a dream.) About 70 ft. down a winding, uneven passage lies Errour, who will sally forth one round later to attack the target PC and his or her allies. During this encounter, all members of the party may act normally save the target PC, who retains her or his hit points but otherwise has only the abilities of a zero-level human commoner. The dream ends when either the target PC or Errour is slain, at which point the target PC wakes up. If the PC was in combat with Errour when the dream ended, s/he gains 1d3 temporary points of Wisdom for the next 24 hours. If the PC was in flight or hiding from Errour when the dream ended, s/he loses 1d3 points of Wisdom for a week. The status of any other PCs involved in the target PC's dream encounter is reset to the moment before the dream; i.e., they retain all the hit points, spells, ammunition etc. from before, as if the encounter had never occurred. The PCs earn no XP from the encounter.
       If the target PC lost points of Wisdom as a result of the encounter, there is a 50% chance that the dream will recur when s/he sleeps again. It is quite possible that in these subsequent dream encounters, the other players will decline to help the target PC for purely metagame reasons; after all, what's in it for them? No treasure, no XP. That's fine! The target PC must nevertheless face Errour as described above, bereft of all abilities save those of a zero-level human. All Wisdom point losses are cumulative. The dream cycle ends only when the PC gains points of Wisdom as a result of facing up to Errour in combat.

Errour for Swords & Wizardry

Hit Dice: One greater than the level of the target PC
Armor Class: 8 [12]
Attacks: Tail sting (1d8 + poison) or constriction (2d4) or or taunt (see below) or vomit (see below)
Special: Poison, constriction, taunt, vomit
Move: 9
Alignment: Chaos
Challenge Level/XP: n/a

Poison: Save vs poison or suffer a -1 penalty to all attacks and saving throws. The effects of multiple stings are cumulative.

Constriction: target must succeed on a saving throw or be held immobile in Errour's coils and take 2d4 points of damage each round. Errour may only constrict one creature at a time and her movement decreases to 6 while doing so. Creatures with combined Strength scores of 30 can force Errour to uncoil and release the victim in 2 rounds, but cannot take other actions during that time.

Taunt: Errour can taunt the target PC, mocking her or his beliefs. This will always be done in the target's native language. The target must succeed on a saving throw or suffer a -2 penalty to all attacks, saving throws, and ability checks for the duration of the encounter.

Vomit: Once per day, Errour can spew out 4d10 small, slimy, gibbering creatures that look like misshapen snakes and frogs to harry her attackers. Her vomit spew has a range of 20 ft. These creatures (AC 8 [12], hp 1, Move 6) cause no damage but as long as at least 4 of them are harrying a creature, the latter suffers a penalty of -1 to attacks and saving throws and cannot cast spells. When Errour dies, her spawn immediately explode, covering creatures within a 5 ft. radius in foul smelling ichor.

Arms of the Serpent by Caroline Jambour

Errour for D&D 5e

Large aberration, neutral evil
__________________________________________
Armour Class 12 (natural armour)
Hit Points Equal to those of the target PC, plus 1d8 hp
Speed 30 ft.
__________________________________________
   STR      DEX      CON       INT       WIS      CHA
14 (+2)   16 (+3)  16 (+3)  18 (+4)  10 (+0)    8 (-1)
__________________________________________
Skills Athletics +2, Deception +4, Perception +6
Senses Truesight 120 ft., passive Perception 16
Languages Any known by the target PC
Challenge n/a
__________________________________________
ACTIONS
Multiattack. Errour can use any two of her attacks each round.

Tail sting. Melee weapon attack: +4 to hit, reach 10 ft., one target. 
Hit: 8 (1d8 + 4) piercing damage and the target must make a DC 15 Constitution saving throw or become Poisoned.

Constriction. Melee weapon attack: +4 to hit, reach 5 ft., one target. Hit: Target must make a DC 15 Dexterity saving throw or become Restrained, taking 2 (1d4) points of damage each round after the first.

Taunt: Errour mocks the target PC's beliefs in his or her native tongue, as long as the target is within 30 ft. The target must make a DC 15 Wisdom saving throw or have disadvantage on all rolls for the duration of the encounter.

Vomit: Once per day, Errour can spew out 4d10 small, slimy, gibbering creatures that look like misshapen snakes and frogs to harry her attackers. Her vomit spew has a range of 20 ft. These creatures (AC 12, hp 1, Speed 20) cause no damage but as long as at least 4 of them are harrying a creature, the latter has disadvantage on all rolls and cannot cast spells. When Errour dies, her spawn explode, covering creatures within 5 ft. in foul smelling ichor.


Errour, by the book

Errour appears in Book I, Canto i of The Faerie Queene. All references are by book, canto, and stanza.

Medusa concept art from the God of War video game

Errour lives in a "hollow cave / Amid the thickest woods" (I.i.11), which is where the Redcrosse knight finds her. Una, his companion, warns Redcrosse that she is "a monster vile, whom God and man does hate" and Una's dwarf cries, "Fly fly ... / ... this is no place for living men" (I.i.13), but Redcrosse is a paladin with Intelligence as a dump stat, so he goes right in anyway. 
      The faint light of his glistening armour reveals her hideous shape: 

... his glistring armor made
A litle glooming light, much like a shade,
By which he saw the ugly monster plaine,
Halfe like a serpent horribly displaide,
But th'other halfe did womans shape retaine,
Most lothsom, filthie, foule, and full of vile disdaine.

And as she lay upon the durtie ground,
Her huge long taile her den all overspred,
Yet was in knots and many boughtes upwound,
Pointed with mortall sting. Of her there bred
A thousand yong ones, which she dayly fed,
Sucking upon her poisonous dugs, eachone
Of sundry shapes, yet all ill favored:
Soone as that uncouth light upon them shone,
Into her mouth they crept, and suddain all were gone.  (I.i.14-15)

So, yeah, she's basically a yuan-ti halfbreed avant la lettre, but with an eery twist: she has a thousand vile offspring that she's nursing and then swallows when Redcrosse shows up, presumably to protect them.

Illustration by Walter Crane from an 1894 edition of The Faerie Queene. Errour can be seen at bottom.

      So the fight begins, and although Errour seems to win initiative in stanza 16, her tail sting attack misses and in stanza 17 Redcrosse  lands a good blow with his sword. Then she switches gears:

Much daunted with that dint, her sence was dazd,
Yet kindling rage, her selfe she gathered round,
And all attonce her beastly body raizd
With doubled forces high above the ground:
Tho wrapping up her wrethed sterne arownd,
Lept fierce upon his shield, and her huge traine
All suddenly about his body wound,
That hand or foot to stirre he strove in vaine:
God helpe the man so wrapt in Errours endlesse traine. (I.i.18)

 Special attack: Constriction! Cf. Snake, giant (constrictor) in the Monster Manual (1979), p. 88-89.
      Unable to use his weapons, Redcrosse is in dire straits. Una advises him to strangle Errour before she can strangle him, and so he grabs for her throat.  At which point she unleashes another gruesome surprise:

Therewith she spewd out of her filthy maw
A floud of poyson horrible and blacke,
Full of great lumpes of flesh and gobbets raw,
Which stunck so vildly, that it forst him slacke
His grasping hold, and from her turne him backe:
Her vomit full of bookes and papers was,
With loathly frogs and toades, which eyes did lacke,
And creeping sought way in the weedy gras:
Her filthy parbreake all the place defiled has.

As when old father Nilus gins to swell
With timely pride above the Aegyptian vale,
His fattie waves do fertile slime outwell,
And overflow each plaine and lowly dale:
But when his later spring gins to avale,
Huge heapes of mudd he leaves, wherein there breed
Ten thousand kindes of creatures, partly male
And partly female of his fruitfull seed;
Such ugly monstrous shapes elsewhere may no man reed. (I.i.20-21)

Apparently she has some kind of breath weapon akin to projectile vomiting that includes slimy misshaped sightless amphibians. (Those "bookes and papers" are a reference to the polemical tracts that Spenser associated with religious error.) Redcrosse is "choked with the deadly stinke" and weakens — seeing which, Errour brings forth her offspring once more:

She poured forth out of her hellish sinke
Her fruitfull cursed spawne of serpents small,
Deformed monsters, fowle, and blacke as inke,
Which swarming all about his legs did crall,
And him encombred sore, but could not hurt at all. (I.i.22)

According to A. C. Hamilton, "sinke" here could refer either to her womb or organs of excretion. Considering that she swallowed her kids in the first place, the latter makes more sense. So basically she defecates on the knight. Good thing his armour seems to protect him from the "deformed monsters" at his feet — Spenser takes a whole stanza to reassure us that they don't bother him more than a cloud of gnats does a shepherd. Evidently these are low hit-dice monsters.

      They do get his ire up, however, and somehow Redcrosse gets his sword arm free and lops old Errour's head right off — critical hit! — amidst great spewing of "cole black bloud." Then comes a gruesome sight:

Her scattred brood, soone as their Parent deare
They saw so rudely falling to the ground,
Groning full deadly, all with troublous feare,
Gathred themselves about her body round,
Weening their wonted entrance to have found
At her wide mouth: but being there withstood
They flocked all about her bleeding wound,
And sucked up their dying mothers blood,
Making her death their life, and eke her hurt their good. (I.i.25)

Yeah, that's right: her kids try to regain the protection of her digestive tract but, frustrated, end up drinking her blood. In fact, they drink so much that in the following stanza they explode, "bowels gushing forth." So ends the encounter. The Redcrosse knight remounts his steed and continues his journey with Una and the dwarf in tow.      

Source:
Spenser, Edmund. The Faerie Queene. Edited by A. C. Hamilton. London and New York: Longman, 1977.