Acid world

Acid world
A pool of acid among salt and sulphur formations at Dallol, in the Danakil Depression of Ethiopia · Hervé Sthioul, CC BY 2.5, Wikimedia Commons

A world of fiction: no known body is like it.

A world where the rain eats stone: the drizzle, the standing pools and the morning mists are acid enough to dull a visor in a day, and they have carved the badlands into fins and arches. Yet the place teems. Rubbery crusts in every colour coat the rock, flocks of leathery flyers wheel and cry over the pools, and larger things hunt them from the ledges. No known world is like this one. Everything brought down from orbit wears out here, and so does anyone who stays outside too long.

Light
Dim
Going
Slow

Hear it

Hazards

  • Acid rain. The rain, the pools and the morning mist are all acid: a drizzle stings bare skin, a puddle softens a boot sole, a day in the open dulls a visor. Every seal, hose and lens wears out, and spare parts are counted like water. D&D 5e (House rule): House rule: a creature with bare skin in the rain or mist takes 1d4 Acid damage at the end of every 10 minutes; one that falls into a pool takes 2d6 Acid damage at the start of each of its turns there. Each day in the open, a sealed suit needs a DC 12 Intelligence check with tinker's tools or it starts to leak, and its wearer counts as bare-skinned until it is mended. Starfinder 2e: Corrosive atmosphere (GM Core): caustic gases bring weather such as acid rain, dealing minor to moderate acid damage (1d6 to 2d6, or 4d6 to 6d6) every minute to creatures and objects. Certain metals, stones and treated materials may resist a given corrosive atmosphere. Archives of Nethys
  • Unbreathable air. There is air, but not air a human can live on: too thin, no oxygen, or the wrong gases. A mask and an oxygen supply are enough where the pressure holds; a full suit where it does not. D&D 5e: A creature holds its breath for 1 + its Constitution modifier minutes (at least 30 seconds), then gains 1 Exhaustion level at the end of each of its turns until it can breathe; it then loses all the Exhaustion it gained this way. Starfinder 2e: Thin atmosphere (GM Core): a few hours make a creature that is not acclimated fatigued; in severely thin air it attempts a Fortitude save every hour or becomes drained 1. With no oxygen at all, use holding breath and suffocating (Player Core). Armour environmental protections cover both. Archives of Nethys
  • Alien microbes. Life that never met a human: most of it cannot touch our chemistry at all, but nobody knows which of it can. Quarantine, filters and patience decide who goes home. D&D 5e (House rule): House rule: a creature that breathes the open air or eats unscanned food makes a DC 12 Constitution saving throw at the end of the day; on a failure it has the Poisoned condition for 1d4 days. A creature that succeeds three days in a row is safe from this world's microbes.
  • Food that is not food. The fruit looks ripe, the fish looks fat, and none of it may be made of anything a human body can use. Some of it is poison; most of it simply does not feed. D&D 5e (House rule): House rule: foraging finds no food a human can live on unless a lab or a DC 18 Intelligence (Nature) check proves it. Living on it otherwise is Malnutrition: a creature that eats less than half its daily food makes a DC 10 Constitution save at the end of the day or gains 1 Exhaustion level.

What may happen

  1. After a day outside, someone's visor has gone faintly milky, and fine scratches catch the light like frost.
  2. At dawn the flyers leave the cliffs all at once, hundreds of them, and their cries echo off the fins of rock for a full minute.
  3. A chain of pools runs down the slope, each a different colour, green, rust and milky blue, each one steaming gently in the cool air.
  4. A boot comes out of a puddle fizzing; the outer layer is softening where the upper meets the sole.
  5. A ledge above the path is crusted with nests woven from something like wire, and the adults on it are watching.
  6. A bank of yellowish mist rolls up the canyon with a sharp smell; where it touches, the crusts on the rocks close up like fists.
  7. A survey drone lies in a gully, its casing eaten to lace; its memory core sits in a sealed pocket that may have held.
  8. A ship passes low overhead, its engines thundering down the canyons. It does not answer the hail, and its hull markings have been painted over.
  9. After the rain, the crusts on the rock swell and open into thousands of tiny cups, each one holding a bead of clear acid.
  10. A soft hiss from someone's suit: a seal at the elbow is failing, and the nearest shelter is an hour away.
  11. Rain has started upstream, and the dry gully the party is walking in begins to trickle, then to smoke.
  12. A flat of white shells crunches underfoot, thousands of them, each as thin as paper and holed by the rain.
  13. Something like a slow armoured slug the size of a cart grazes the crust off a boulder, leaving the stone bare and clean behind it.
  14. One pool lies perfectly still while the rain dimples every other pool around it.
  15. A ring of anchor bolts in the rock marks where a camp once stood; nothing else is left of it but one sealed canister, still closed.
  16. At night something calls from far up the canyon, a long falling note, and every flyer on the cliffs goes silent.
  17. Where a pool has dried, the ground is a crust of crystals that rings like glass underfoot.
  18. Fresh grooves cross the path, as wide as a person and as deep as a hand, still wet and smoking.
  19. A young flyer is caught in a crack of rock, one wing torn, screaming, while adults circle overhead.
  20. The solar panels left out overnight give half their usual power; a grey film has settled on every cell.
  21. The path runs under a thin arch of rock, eaten through by the rain until daylight shows in a dozen places.
  22. Someone's sample jar of pool water has turned, overnight, from clear to deep violet.
  23. A distress beacon sounds on an old frequency from beyond the next ridge, repeating a call sign nobody on board recognises.
  24. A flyer dives at the party and pulls up at the last moment, dropping a gob of something that sizzles on the rock.
  25. A spring in the rock runs with water the meter reads as almost neutral, the first in days; the crusts around it are a different colour.

Adventure hooks

  1. A mining consortium wants samples from the deepest acid lake, and its last team's suits were found empty on the shore.
  2. A naturalist pays well for a live flyer, and the whole flock defends its young as one.
  3. The ships flying low through the canyons belong to someone who has filed no landing claim.
  4. The rain is growing weaker every year, and the refinery that lives on its acid wants to know why before its investors do.

Who and what is met

Each is an SRD stat block under another name, as game masters reskin them.

Other worlds

Cold desert world, Ice moon with a hidden ocean, Methane world, Hothouse world, Volcanic world, Airless world, Ocean world, Tidally locked world, Earthlike world, Jungle world, Swamp world

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.

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