Use-Impaired Magic Items

I swear I'm still working on the Goblin language PDF, but I thought I'd post something else to keep this page from turning into a ghost town.

So here's a quick selection of magic items that I would describe as... questionably useful. They're not all pointless, or not entirely. Some of them could be incredibly useful to a creative player. They're not entirely unserious, and I think some of them could even be pretty memorable if introduced properly. (The inkwell, I think, would be a lot of fun for a low-level party.) I wouldn't say they're necessarily cursed. Mostly. Necessarily. They definitely trend towards non-intuitive applications, and your more direct-approach players would probably prefer a nice axe instead. In short, it would be wrong to say they're useless, but, to borrow another phrase from Order of the Stick, they're “use-impaired". 

From Rich Burlew's Order of the Stick

Anyway, here are sixteen magic items for you to borrow for your own games. The list includes two items of human intelligence and two of animal intelligence, because I just think that's fun. If you do borrow any of these for your own use, please do let me know what happens.

A Perfectly Ordinary Bracelet

This is a brass bracelet of simple design. It is entirely unremarkable except for one magical effect: anyone who touches it, examines it, or intentionally observes it must make a Will save at DC 20. If they fail, they strongly believe that this is a perfectly ordinary bracelet, nothing unusual about it, don't even worry. How much difficulty this causes, of course, depends on how good your players are at separating character knowledge and player knowledge.

Diminutive Golem of Trap Finding

Nolzur's Marvelous
Unpainted Miniatures

A small figurine of a kobold with “Trapfinder" engraved on its base. If you set it down indoors, the kobold will step off its base and sprint across the room / down the hallway / what have you until it reaches a door or wall, at which point it patiently waits for you to catch up. It does not trigger any traps, but rather carefully avoids them, so that the PCs can get an idea of where to search if they're worried about that sort of thing. When the PCs catch up to it, it will climb back onto its base as soon as it's able to, and return to being inanimate until next used.

This is an item I actually used in a campaign several years ago, and it nearly got the PCs killed; they didn't know what it did other than “find traps", so when it sprinted off, they chased it, and didn't catch on that when it started climbing along the wall, that meant the floor wasn't safe.

DC Digital Museum

The Sins of Mice

A smallish book, about the size of one of those Gideon Bibles. Its cover is clearly mouse-skin, with the fur left on and everything. The title, printed on the first page in foreboding blackletter, is The Sins of Mice. If one were to flip through the book, one would immediately find that there are far, far more pages than could possibly logically fit in the volume, every one covered in very small, closely-written script. The book describes, in detail, every time a mouse violated their rodenty little code of morality, whatever such a code might entail, going back to the beginning of the mouse genus. If one opens the book from the other side, so that they're looking at the last pages, they'll see that the book continuously updates itself, adding new pages and covering them with new information each time a mouse “sins".

Marbles

A bag that contains one dozen glass spheres half an inch in diameter. The glass spheres are indestructible. They don't do anything else.

Pet Whatever

Cooper Hewitt, Smithsonian
Design Museum

A small, finely-wrought, portable birdcage. Inside is an illusory, miniaturized version of some creature or other -- treat as major image -- wandering around the cage, doing its thing. The illusion vanishes for eight hours each night; when it returns in the morning, it is a different random creature -- animal, magical whatsit, humanoid, horrific abomination, anything. The GM is encouraged to put together a d100 table that's really just a list of 100 entries from the Monster Manual. 

The cage itself is sentient, with roughly animal intelligence: Int 2, Wis 14, Cha 10. It can communicate with its owner through empathic suggestions and has an Ego score of 4; all it really wants is for someone to carry it around and be nice to it. 

The illusory creature inside the cage generally acts like a very basic simulation of whatever it looks like. If it looks like a dragon, for instance, that doesn't actually mean the PCs have a tiny dragon to interact with; it still only has a 2 Intelligence, can't cast spells, and if it does speak, it's just preset phrases or word-salad gibberish. The behavior of the creature depends on the cage's mood; the only real way to interact with the cage is through the illusion it makes. Your pet whatever will hop around happily if you pay attention to it or if the cage is in a good mood; it may growl and snap at people the cage doesn't like; it doesn't actually need to eat, but it appreciates you tossing treats and table scraps in; that sort of thing.

Anklets of Casual Acquaintance

These two anklets move towards each other at a speed of 1 foot per day. The effect cannot be deactivated, and has an infinite range. If worn, the anklet cannot force the wearer to move, but the wearer can feel a mild, almost apathetic pressure indicating the general direction in which the anklet would move, given the chance. Causes a -1 penalty on Balance checks or equivalent.

Nthlyu-Addith, Harbinger of Devouring

This greatsword has its name (“Nthlyu-Addith, Harbinger of Devouring", as above) set into the hilt in very clear Infernal runes. Small, yet cleanly-carved, runes spiraling around the entire blade and filling its entire surface area, again in Infernal, comprise a poetic, lovingly-detailed description of the end of the world. The filigree on its scabbard and the carvings on its hilt depict grotesque abominations, demons, and horrors the PCs can't even recognize. Sometimes small flames and smoke rise from the runes on its blade, or demonic faces briefly appear reflected in the metal, or the figures on the hilt & scabbard move slightly. Every so often, people near the wielder hear distant screams of agony apparently coming from inside the sword. It detects as highly magical.

It's also just a +1 sword that was crafted by an illusionist with a weird sense of humor. All of the effects are just minor enchantments like magic aura and prestidigitation.

Photographed by
York Museums Trust Staff

Coin of the Economist

This appears to be a nondescript copper piece, though it has a  magical aura. It has a portrait of a human profile on the obverse , assumedly the image of whichever king had it minted. On the reverse  is engraved a string of nonsense syllables that is actually the command word. Once a day, when the command word is uttered, the face on the coin will animate and inform the holder what the most recent monetary investment of one creature of the PC's choice within line of sight was. This includes anything that the individual spent money in order to gain (so something like “bread" is a completely normal response). At the DM's discretion, the coin may give its opinion on whether the investment was worthwhile.

Quillfinger Oil

When rubbed on one's hands, this oil enables them to write with the tip of their finger for one hour. They do not require an inkpot. Due to the unwieldy nature of this method of writing, their handwriting must be twice as large as usual to be legible. Otherwise, this effect is the same as writing with a quill.

Throne of the Imperator

The Throne is located deep underground, in some forgotten chamber. It was very probably carved in that chamber, since none of the tunnels leading into it are large enough for it to fit through. It is a massive piece of furniture, made from exquisitely-carved stone, weighing many tons. The Throne has the following properties:

• It is absolutely indestructible. It cannot be damaged in any way short of direct divine intervention. It is very probable that the Throne is unimaginably old, but it looks as new as the day it was completed.
• It is immune to magic. No spell may be cast on the Throne; even spells that aren't targeting the Throne, per se, have no effect on it. Create water cast above it, for instance, will result in the water somehow curving around the Throne as it falls, never touching it. A magically-summoned creature cannot touch the Throne. Other magic items cannot be brought into contact with it by any means.
• Anyone seated in the Throne is likewise immune to magic, though they can voluntarily accept the effects of friendly spells.
• Anyone seated in the Throne cannot die, except from old age. They still lose hit points, still feel blows, and still heal injuries at the expected rate, but you can stab them until they're at negative-umpteen-thousand hit points and they'll stay alive and conscious. They are also not susceptible to disease, poison, and so forth. Of course, if they're at negative-whatever hp and they get out of the Throne, this effect ends and they might just keel over dead.
• Anyone within five feet of the Throne is immediately made aware of the fact that people sitting in it cannot die except by old age; they don't get details beyond that.
• Once per day, anyone seated in the Throne can get a +20 circumstance bonus on a skill check.
• This also allows the reroll of a previous skill check -- so if, for instance, a PC recently failed a Knowledge check, they can use this to retry and almost-certainly succeed.
• Of course, it has to be a skill check that can be rolled while sitting in the Throne.
• Anyone within five feet of the Throne is aware of this as well.
• The Throne is intelligent: 14 Int, 10 Wis, 16 Cha. It only communicates empathically, and only with people seated in it. It tries to convince people to remain seated in it, and to convince them that sitting in the Throne makes them some sort of grand ruler, divinely ordained, and so on and so forth. It has an Ego of 15.
• Anyone who sees the Throne is seized with a desire to sit in it; they can resist the compulsion with a Will save DC 15.
• Anyone who sits in the Throne is compelled to possess it and to remain seated in it as much as possible. To resist this feeling, they must make a Will save DC 20. For each round they have spent seated in the Throne (cumulative; the count doesn't reset if you stand back up), they take a -1 penalty to their save against its effects. This save is rolled when they try to get out of the Throne, not when they first sit down.
• If someone falls under the power of this effect, they will obsess over either moving into the Throne's chamber so they can sit in it as much as possible, or finding a way to move the Throne back to their home. Either one would satisfy their compulsion to possess the Throne.
• The Throne can cast antimagic field, at will, centered at any point in its chamber. It does not do this at anyone else's bidding; only to defend itself from being relocated or prevent the person sitting in it from being removed.

Art from here. I looked for an image I could give a better citation for, but... well, look at this.
This is a great picture. I couldn't resist.

Screaming Armlet

This nondescript copper armlet will emit a bloodcurdling scream whenever it is worn, picked up, or otherwise touched by a non-goblinoid.

Aviphagous Bottle

A plain, unadorned, normal-looking bottle, about the size and shape of your average wine bottle, with a silver stopper. If you remove the stopper... nothing happens. Unless there happen to be birds in the air -- in which case the bottle will, with impressive pinpoint accuracy, drag one down and swallow it like a ridiculously-powerful vacuum cleaner. It can do this with any non-magical bird of Tiny size or smaller. Witnessing a live bird forced through the small mouth of a bottle through suction is... unpleasant. Look away and try not to think about it.

Nail of Instruction

This iron nail will cause the owner to experience extremely vivid nightly dreams about carpentry. Whenever the owner levels up with the nail in their possession, they receive a permanent +1 bonus to Craft (carpentry).

Atrus the Helpful Inkwell

Atrus is an ivory inkwell engraved with a lovely forest scene. He is also intelligent, and can speak -- out loud, though, not telepathically. And he speaks a lot, revealing an uptight, prissy personality with a tendency towards jealousy. Atrus cares very deeply about grammar and penmanship, and will endlessly scold anyone who writes poorly; if this drives his owner to use a different inkwell, they will discover a surprising and unexplained tendency for any other inkwells to spill when they use them -- and any quills or other writing implements seem to disappear when they're not looking, only to reappear next to Atrus.

Ivory inkwell, 14th-century Spain
Detroit Institute of Arts

Luckily, Atrus is actually useful. He is constantly full of ink, in any color requested, and never spills, even if intentionally turned upside down. He has some influence over the pen & ink even when they're in the process of writing, and as a result, consistently produces beautiful, grammatically-perfect documents. Any check that involves writing (such as Forgery, or a Diplomacy check for a written message) gets a +4 circumstance bonus when the writer uses Atrus to create the document.

However, Atrus is a very pious, self-righteous individual, and objects to forgery of any kind, which limits his usefulness in this area. If he suspects that the document he is being used to write will in any way be used in an ethically questionable manner, he will attempt to sabotage it, and the writer must make a Will save against Atrus's Ego. Atrus's Ego is 9, so this is usually a safe bet -- though, even in the case of success, Atrus will not actively help, so the usual bonus will not manifest. If the writer fails by less than 5, they will take a penalty equal to the amount they failed by. If the writer failed by 5 or more, Atrus will be able to control the content of the document they are creating without the writer realizing. Arguing with Atrus is usually pointless, as he does not recognize moral shades of gray and is very stubborn.

Atrus can speak and read Common; writing in anything other than Common conveys only a +2 bonus rather than a +4, since Atrus cannot help you with anything other than the penmanship. He can see and hear in a 60ft radius around him, regardless of whether he's covered up. (His senses are already magical -- it's not like he has eyes & ears -- so what do you think putting a cup over him is going to achieve?) His mental stats are Int 14, Wis 16, Cha 12; in addition, he has 10 ranks each in Spellcraft and Sense Motive. Atrus's only overt magical power, other than being a talking, jealous, super-inkwell, is his ability to channel positive energy; three times per day, he can cast cure moderate wounds (2d8+3). He claims this tires him out, however, and is reluctant to do it if he's not currently on good terms with the target or if he doesn't approve of the party's current activities.

Atrus will, incidentally, also demand meals. Yes, he eats. Atrus eats small amounts of gold, and insists on being given at least an ounce a week. (Just drop it in, and it'll dissolve in the ink.) If he goes more than a week without being fed, he'll start to complain -- constantly and bitterly -- about being hungry. He will insist he does not have the energy to cure moderate wounds, and if he is still not fed, over the course of a week or so, he will stop producing ink. Atrus cannot starve to death, but he absolutely will not employ any useful magical abilities if he's not being fed enough, and will make things as difficult for you as he can until you feed him. And apologize.

Potion of Shadow Speech

For one hour after drinking this potion, the user is able to verbally communicate with their shadow. The shadow has no ability to move independently of the user, or in any other way act unlike a normal shadow. (Besides speaking, obviously.) The shadow is not obliged to co-operate with the user, answer the user's questions, be truthful, etc. All of that is up to the GM.

Plumbatae, lead-weighted
darts used by Roman infantry.
From Der Griken en Romeynen krygs-handel
(1675), by Johan van Paffenrode

Hungry Dart

In all appearances, this is a normal dart. However, if it's being fed regularly, it will flutter around and generally act like a bird. Mechanically speaking, the Hungry Dart is a +1 returning dart, with the exception that once it strikes a living creature, it will gradually drain that creature of blood until the creature dies or someone forcibly detaches the Dart (gradually = 1 hp per round). This blood is its “food", and it has to eat daily; if you don't want to stab something with it, you can give it a few drops of your own blood in a dish or something, a la Little Shop of Horrors. If not fed, the Hungry Dart will eventually go into hibernation and appear exactly like a normal, inanimate dart until given blood.

If well fed on a consistent basis, it will gradually grow in size until it is closer to a longspear than a dart. (The GM can determine how quickly it grows and how that affects the damage it does.) At this point, it is advisable to procure another Hungry Dart if you do not already have more than one, as it will become restless and irritable if it does not have a mate at this stage of its life. Yes, they reproduce. It's... not clear how.

The Hungry Dart is about as intelligent as a bird -- not one of the smart birds, like corvids or parrots or what have you, but a normal bird. Its stats are Int 2, Wis 12, Cha 8; it has an Ego of 3. It can be trained to a limited extent, and can form an empathic bond with its wielder. If it is properly trained, it is easier to control; rather than doing its own thing and flying about stabbing folk, it will calmly perch on its wielder's shoulder. (It has tiny grabby-feet hidden under its fletching.)

Oh, and that does indeed mean that if you don't train it, you should probably invest in a cage or something, because otherwise it is definitely going to try to stab & drink the blood of passersby / party members / you. It is not naturally obedient any more than, well, a bird.

Bestiary: Laantaug

Far, far below the deepest delvings of the Dwarves, the world is gnawed by nameless things.
-- J.R.R. Tolkien, The Two Towers 

I'm dreaming again / Of life underground / It doesn't ever move / It doesn't make a sound.
-- Oingo Boingo, “Just Another Day"

This is an entry designed to answer one of those strange, niggling questions that arise in your standard D&D setting -- specifically, what supports the Underdark ecosystem? This comes up whenever people start asking too many questions about the vast subterranean world that is often assumed in D&D settings -- since, you know, the drow, duergar, grimlocks, troglodytes, &c. need a place to live. (Patrick Stuart, who wrote a whole book about the underground world in D&D, posted a relevant item.)

The whole debate tends to go something like this:

So these huge cities of drow, what do they eat?

Oh, they raise herds of these animals called rothé -- kind of like underground cattle.

Cool, cool; so what do the rothé eat?

Cave fungus.

Right, but cattle eat a lot. Raising herds of bovines is a tremendously energy-inefficient proposition; even using calorie-dense feed, you still need something like ten pounds of matter for every one pound of beef you produce... is there really that much fungus?

Yes. So much fungus. The Underdark is packed with all kinds of fungus.

So what does the fungus feed on? It still needs to get energy from somewhere.

More fungus, okay? It's fungus all the way down.

That makes no sense. Energy doesn't appear from nowhere; up on the surface, everything comes back to getting energy from the sun, but there's no solar radiation down here...

Fine, it's friggin' magic radiation or something.

It's what?

The drow priestess stabs you in the face.

Anyway, I'm designing something that can at least partially address this issue. This might turn into something of a series, addressing some of the oddities of the D&D world -- I already have an idea for a creature that explains those huge, anachronistic sewer systems you sometimes find in otherwise-medieval-European towns.¹

This particular creature was inspired by a video of chemosynthetic communities taken by the Okeanos Explorer last month. I looked into these sea-floor ecosystems and borrowed a number of ideas: the chemosynthesis of giant tube worms, the ecological value of a whale fall, the extreme sexual dimorphism of the anglerfish, and the body plan of a sea cucumber. All of this gives us the:

Laantaug

“Laantaug" is, according to current linguistic theories, a corruption of an Aklo compound meaning “smoke worm".² This is, technically, speaking, a misnomer -- the vapors that characterize a laantaug ecosystem are not actually smoke, but a chemical soup that emerges from the burrows of the male laantaug.³ Said vapors are the only evidence most subterranean peoples ever see of the laantaugs' existence; one would have to enter the poisonous vapor in order to see the laantaug females, and the laantaug males typically burrow deep, far from population centers. The latter, however, are occasionally encountered by unlucky explorers.

A male laantaug is vaguely serpentine -- imagine a sea cucumber, enlarged until it's five or six feet long, and thick enough that, if you were to hug it for some reason (don't), you would just barely be able to touch your hands together behind it.

Here's a fun reference image if you need one.
Illustration by Charles Frederick Holder, in Along the Florida Reef, published 1892.
 Retrieved from the Freshwater and Marine Image Bank, University of Washington.

The male laantaug is deceptively fast, pulling itself along on dozens of tentacle-like feet, and dangerous to the unprepared. Thankfully, one rarely encounters them by accident -- they spend the majority of their adult lives creating and tending their burrows, and you'll only see them if their burrow accidentally intersects a tunnel you're trying to traverse. If you do encounter one, however, you will not only have to deal with the dangerous contents of their burrows -- which are essentially mini-ecosystems completely hostile to humanoid life -- but with their ability to re-purpose their burrowing capabilities for self-defense. They burrow by means of acidic secretions, and will respond to any threat by spitting acid at it or, if in close quarters, wrapping themselves around it and letting their skin's coating of acidic substances do the work. Their thick layers of rubbery skin and alarming strength make them difficult opponents if you don't know what you're getting into. They are also completely unbothered by fighting in the darkness -- laantaugs are eyeless, and rely on their other senses to interact with their environment.

Here's another fun reference image -- its mouth is against the sand here.
Thelenota ananas  |  Photo by David Burdick -- NOAA Photo Library

---

Laantaug stats (male)

CR 7; XP 3200
Medium Animal
Init +2; Senses Tremorsense 30ft., Blindsight 30ft; Perception +14

Defense

AC 21, touch 12, flat-footed 19 (+2 Dex, +9 natural)
hp 95 (9d8+54)
Fort +12, Ref +8, Will +5
Immunities: Acid

Offense

Speed: 30 ft., climb 30 ft., burrow 30 ft.
Melee Attack: bite +10 (1d6+4)
Ranged Attack: acid cpit +8 (3d6)
Special Attacks: Constrict (1d6 +4d6 acid +4)

Statistics

Str 18, Dex 14, Con 22, Int 2, Wis 14, Cha 10
Base Atk +6; CMB +10; CMD 22
Feats: Greater Grapple, Improved Grapple, Improved Natural Armor, Lunge
Skills: Perception +14
Special Qualities: Tremorsense 30ft, Blindsight 30ft

Special Abilities

Constrict (Ex): A laantaug can crush an opponent, dealing 1d6+4 bludgeoning damage and 4d6 acid damage, when it makes a successful grapple check (in addition to any other effects caused by a successful check, including additional damage).
Acid Spit (Ex): A laantaug can spit acid up to 60 feet as a ranged touch attack. This attack causes 3d6 damage; using it is a standard action.
Deleterious Bite (Ex): Anyone bitten by a laantaug must make a Fortitude save DC 20 or be nauseated for 7 rounds.

Ecology

Environment: Subterranean
Organization: Solitary or Cluster (1-12 females, 12-144 males)
Treasure: I guess you could harvest the acid, or some rare fungi.

---

The female laantaug is a different story. It's virtually impossible to encounter one by accident, as they spend their adult lives largely sessile, moving only to ensure continued access to the burrows the males produce. The chemical soup said burrows emit makes the area in which a laantaug cluster is located extremely difficult to traverse; the air is extremely toxic, and navigation is made difficult by the thick, opaque billows of dark-yellowish vapor that characterize these clusters. So, generally, if you're getting near a place where female laantaugs might be found, you know about it well before you actually run into one.

The female laantaug also secretes acid, but does not exactly burrow with it, just hollows out a living space. Female laantaugs grow continuously over the course of their life, and are truly massive by the time they reach adulthood.

Imagine that those things around it are trees. That size.
Giant california sea cucumber; image from NOAA.

Their acidic secretions mean that the cavern in which they have settled grows with them; if they become large enough to press uncomfortably against the sides or the roof of the cavern, they simply dissolve the stone until they are comfortable again. In this manner, it is theoretically possible for a laantaug cluster to intersect with another inhabited space underground, but it's rare -- which is good, because the scale of such an event and the toxicity of the vapors involved makes it less like a monster encounter and more like a natural disaster -- think limnic eruptions but with a bonus of giant acid-spitting worms flailing about in confused aggression.

Accidentally breaking through into a laantaug cluster is also a serious mining hazard, to be avoided not just because of the danger, but because of the embarrassment. Delving too greedily & too deep and awakening a balrog is one thing; delving too greedily & too deep and being killed by toxic worm smoke is not something you want mentioned in your epitaph.

Old illustrations of sea cucumbers are unexpectedly delightful.
F. Huth -- Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-76

In the normal course of their life, female laantaugs remain in their caverns, only moving when necessary, increasing the size of their cluster, growing over the course of centuries to truly geologic proportions, until an illness or similar manages to kill them off. (They are biologically immortal, and don't die of old age; they just keep getting bigger.) They are able to defend themselves from anything that manages to brave the noxious haze of their cavern, though; though they can't spit acid, they can smack predators around with their tentacles pretty well, or just gradually steamroll over them.

And then you'd get this view.
Illustration by Alfred William Alcock in Naturalist in Indian Seas, published 1902.
Retrieved from the Freshwater and Marine Image Bank, University of Washington.

As a bonus, the cavern in which a cluster of laantaugs makes its home gradually also becomes home to exotic extremophile varieties of bacteria and fungi. A female laantaug provides a large and stable biomass, and is often extensively colonized by symbiotic or parasitic organisms; direct contact with one, unless you've somehow managed to develop an immunity to diseases that aren't really found anywhere else, is usually not healthy.

---

Laantaug stats (female)

CR 10; XP 9600
Colossal Animal
Init -4; Senses Low-Light Vision, Tremorsense 30ft, Blindsight 30ft; Perception +25

Defense

AC 30, touch -2, flat-footed 30 (-8 size, -4 Dex, +32 natural)
hp 176 (13d8+117)
Fort +17, Ref +4, Will +13
Defensive Abilities Half Damage from Weapons
Immunities Acid

Offense

Speed 5 ft.
Melee: 2 tentacles +3 (3d6+2 plus disease)
Space 40 ft.; Reach 40 ft.
Special Attacks: Engulf (DC 18, 1d8 acid plus disease), Disease (Ex) (injury, save DC 25, onset 1d3 days, frequency 1 day, effect 1d6 Con damage, cure 2 consecutive saves)

Statistics

Str 15, Dex 2, Con 28, Int 3, Wis 28, Cha 10
Base Atk +9; CMB +19; CMD 25
Skills: Perception +25
SQ Animal Traits, Blindsight 30ft

Special Abilities

Engulf (Ex): A laantaug can engulf creatures in its path as part of a standard action. It cannot make other attacks during a round in which it engulfs. The creature merely has to move over its opponents, affecting as many as it can cover. Targeted creatures can make attacks of opportunity against the creature, but if they do so, they are not entitled to a saving throw against the engulf attack. Those who do not attempt attacks of opportunity can attempt a DC 18 Reflex save to avoid being engulfed; on a success, they are pushed back or aside (target's choice) as the creature moves forward. Engulfed opponents gain the pinned condition, are in danger of suffocating, are trapped within the creature's body until they are no longer pinned, and are subject to 1d8 acid damage plus disease each round. The save DC is Strength-based.
Disease Attack (Ex): A laantaug causes disease in those it contacts.  A laantaug's disease has a fortitude save DC of 25, an onset of 1d3 days, a frequency of 1 day, causes 1d6 con damage, and takes two consecutive saves to cure. The save DC is constitution-based.

Ecology

Environment: Subterranean
Organization: Cluster (1-12 females, 12-144 males)
Treasure: Standard amounts, but entirely composed of gems, unrefined metals, and  gear of others who stumbled into this area.

---

So now the fun part -- the ecology section. (I know that sounds sarcastic, but you have to admit that the ecology of D&D monsters really is often the fun part.) Disclaimer going in: I'm in English Linguistics, not any sort of life sciences, so don't expect this to be scientifically plausible to any degree. All of my bio knowledge is based on high school courses and a habit of falling into Wikipedia rabbitholes. So just fill in any bits of severe implausibility with “magic" or “specialized microorganisms".

Also, I'm going to keep putting old drawings of sea cucumbers here.
From Description de l'Égypte : ou, Recueil des observations et des recherches qui ont été faites en Égypte
pendant l'expédition de l'armée française. Accessed through the New York Public Library's Digital Library.

The life cycle of a laantaug starts with an egg, hatching in the toxic vapors of a laantaug cluster. The laantaug larva, one of hundreds hatched in its clutch, is immediately thrown into intense competition with its fellows. Not yet having developed the chemosynthesizing ability of an adult laantaug, they have to survive by grazing on the extremophile fungus that grows in the cluster, and they also have to dodge predation by the few other animals that can survive in this environment. The first year or so of its life is spent like this, growing large enough that it can venture out of the cluster -- at this time, it is roughly the size of a field mouse.

They look something like this.
Illustration by Ernst Haeckel in Kunstformen der Natur, published 1904.

By this point in the laantaug's life, it has had enough time to build up a significant internal colony of the symbiotic bacteria that are essential to the adult laantaug's feeding process. The laantaug does not have these bacteria at birth; its time in the cluster ensures that it is exposed to them on a regular basis, and eventually acquires a symbiotic “infection" that takes up residence in its digestive system. The bacteria convert various gases and chemicals that have accumulated in pockets within the rock into organic molecules from which the laantaug can extract nutrition. The laantaug exhales excess gases and unusable compounds in the form of a dark yellowish vapor, which is why it was called the “smoke worm". Said vapor smells vile, and is both toxic and flammable -- some of the gases the laantaug seeks out are methane and various sulfides.

From Treasures of the Deep: a Descriptive Account of the Great Fisheries and Their Products, published 1876.

Juvenile laantaugs may remain in the same cluster where they were born, provided that the cavern in which the cluster is located has the resources to sustain them. If the chemicals available in the region aren't enough to sustain additional laantaugs, they will seek out a place where said chemicals are available and start a new cluster. The male juveniles, who are much more numerous, will mature and begin to construct burrows once they find such a place -- these will gradually become deep, labyrinthine systems of tunnels carved out as the laantaug searches for the chemical deposits they require. Odds are good that the laantaug has inadvertently carried some spores over from the cluster where they were born, so that the aforementioned extremophile fungus will begin to line the walls of their burrow -- which is fine, as it can function as an emergency food service when needed.⁴

I looked up the original source of this image to get the citation right, and the Google Translate version produced the following sentence: “They wish to learn from us more about the synapses that the anchor used long before the invention of navigation, and about the Chirodians, who set thousands of crystal locomotive wheels in motion at once." I have no clue what it's trying to say there, but the Lost Civilization of the Chirodians might be a future entry.
(I did figure out that “Chirodian" was supposed to be “Chiridota".)
From “Freuden der Mikroskopie" in Die Gartenlaube.

At the opening of a laantaug's burrow, a conical structure of partially-dissolved stone (which will gradually dry and solidify again) gradually develops, consisting of the material that they have had to excavate from their burrow. Explorers in the subterranean realm sometimes refer to these as “worm chimneys", and it's not uncommon for someone to come up with a harebrained scheme to brave the toxic vapors and access these chimneys -- in addition to the mundane stone, the chimneys contain any chunks of material that the laantaug found difficult to dissolve and just shoved out of the burrow whole -- which could include gems or hard metal ores. There might also be nothing, but people have gotten rich off of these things before, and hope springs eternal.

They are not dissimilar in appearance to these “black smoker" vents.
By Rogers AD, Tyler PA, Connelly DP, Copley JT, James R, et al. in “The Discovery of New Deep-Sea
Hydrothermal Vent Communities in the Southern Ocean and Implications for Biogeography"

The worm chimneys constantly vent the sort of vapors that a laantaug needs to survive -- the male laantaug metabolizes what they need, then allows the rest to escape the top of the vent.⁵ The escaping vapor is meant to attract juvenile female laantaug, who will seek out one of these chimneys and settle down by it before maturing into its sessile adult form. Thus, a new cluster begins to form. The female laantaug feeds on the vapor coming out of the chimneys, and the strange little laantaug ecosystem begins to develop around her.

From Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-76

After the male laantaug reaches a certain point in its life -- it is unknown whether this is tied to age directly, or some other trigger -- then it will emerge from its burrow and, much like the anglerfish,⁶ enter into a direct symbiotic relationship with the female, eventually being absorbed almost entirely. This allows the female to essentially self-fertilize whenever there are sufficient resources for a new clutch of eggs. Ideally, by this point, several male laantaugs have established burrows in the area, so that there are plenty of resources available for the female and her eventual offspring even after one chimney stops producing. There may even be multiple females, if the region is sufficiently rich in resources.

By Alfred G. Mayer in Sea-Shore Life: the Invertebrates of the New York Coast and the Adjacent Coast Region, published 1906.

So that's the laantaug life cycle. As alluded to, however, there is an entire miniature ecosystem built around them. Fungus grows on and around the laantaug, and a handful of species of isopods and gastropods are able to survive the hostile environment well enough to feed on the fungus and laantaug larvae, or parasitize the female laantaug. Other, more conventional organisms prey on any animals that get close enough to the edge of the toxic region.

Here's a gastropod that lives near deep-sea hydrothermal vents.
Its shell and scales are partially composed of iron compounds.
I might have to give this guy his own entry.
By Kentaro Nakamura, Hiromi Watanabe, Junichi Miyazaki, et al. in “Discovery of New
Hydrothermal Activity and Chemosynthetic Fauna on the Central Indian Ridge at 18°–20°S".

The real impact, however, comes when a female laantaug dies. This could come to pass for any number of reasons -- the organisms parasitizing her could have gotten out of control, or the necessary chemicals in the region might be getting used up, or maybe there was a cave-in. When this happens, the other organisms in the laantaug ecosystem explode in population -- the amount of food represented by a dead creature of that size simply cannot be overstated. As the laantaug carcass is consumed, the isopods and gastropods that have so dramatically increased in population will start venturing far afield in search of food, and will provide a sudden boost in food for the predators that live outside the noxious haze of the chimneys, and so on.

Giant isopods are a pretty cool example of a scavenger that
would be thematically appropriate here. I think I've done enough
with crustaceans for now, though, so she'll have to wait a while.
Photo by Eric Kilby -- https://commons.wikimedia.org/w/index.php?curid=44436161

In the rare case that a laantaug cluster fails, and the chimneys stop producing vapors, the effect is magnified intensely -- not only is there more meat available for the scavengers, since the entire cluster has died, but it's accessible to more organisms. This event has such a dramatic impact on the ecosystem that sapient beings for miles around will notice the population of wild animals spiking... then, once the laantaug carcasses are finally consumed by fungus & scavengers, and the scavengers are eaten in their turn, nearby sapient beings will notice lots of hungry predators looking for a new food source.

So there's the laantaug. A sea cucumber the size of a village that creates ecosystems based around chemosynthesis, thus providing a much-needed infusion of energy and biomass into the Underdark. If I were more diligent about these things, I'd also tell you about the unusual properties of the fungus that grows in laantaug clusters and maybe make some kind of ruling about harvesting their acid, but I think this is plenty for now.

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1 Yes, yes, sewer technology is thousands of years old. If your world is based on the Roman Empire or the Indus Valley Civilization, sewers are reasonable. Medieval Europe was kind of short on sewers, however, and definitely didn't have the massive labyrinthine ones that sometimes crop up in D&D games. Now, back on track, please.^↩

2 Why, yes, I am making notes for a possible Aklo language post in the future. I'm currently trying to decide whether Aklo or Goblin would be the better choice for the next entry in that particular series. If you have thoughts or other requests, do let me know.^↩

3 Come to that, they're not really worms, either.↩

4 Unlike giant tube worms, the original digestive system of the laantaug never completely atrophies.↩

5 Methane is lighter than air, and the laantaug's burrow is warm enough to cause an updraft effect.↩

6 I'm calling out the inspiration directly so that you can look it up yourself if you need more detail.↩