The Vhal are a swarm of living darkness that eats aether. A person they touch becomes a husk, an empty body that walks and obeys. Places, ships and objects they touch stay cold and dark. Being near these things wears a creature down.
A Vhal site is a place the Vhal have touched. A cold spot on a ship is one. So is a drifting ship with a husk crew, or a room full of black crystal. The dead world of Hush and the space near Rim Gate Seven are the worst. The GM decides how strong a site is.
Weak. Save DC: 10. Example: A single cold spot, a few black crystals.
Strong. Save DC: 13. Example: A husk ship, a mine full of black crystal.
Deep. Save DC: 16. Example: The surface of Hush, the space near an open Rim Gate.
Exposure Saves. At the end of each hour in a Vhal site, a creature makes a Constitution saving throw against the site's DC. On a failure, it gains 1 Exhaustion level. A creature that is in Bright Light from a lamp or a spell has Advantage on this save.
Exhaustion That Stays. A creature can't remove Exhaustion gained from Vhal exposure by resting while it is still in a Vhal site. Once it leaves, it removes those levels in the normal way.
Cold. The air is much colder than it should be. Nonmagical flames and lamps burn low and give only Dim Light.
Hard Casting. When a creature in a Strong or Deep site casts a spell of level 1 or higher, it makes a DC 10 spellcasting ability check. On a failure, the spell does not take effect. The action is lost, but the spell slot is not spent.
Dead Crystal. Aether crystals and crystal cells carried into a Deep site lose power. At the end of each hour there, each cell loses 1d6 rounds or charges. A cell with none left turns black.
A creature that carries black crystal makes a DC 12 Wisdom saving throw when it finishes a Long Rest. On a failure, it gains no benefit from that rest. Some cursed items made of black crystal follow their own text instead.
Husks and Vhal creatures deal Cold or Necrotic damage, as shown in their stat blocks. Their touch does not cause exposure saves on its own.
A Humanoid killed by a Vhal creature, or one that dies while it has Exhaustion from Vhal exposure, can rise as a husk. It rises 1d4 hours later, or sooner if a stat block says so. It does not rise if the body is burned or blessed by a priest first. A Corpse Stasis spell cast on the body also stops it. Once a body becomes a husk, the person is gone. Raising magic does not bring them back.
Holy light burns husks and drives back the Vhal.
Husks and many Vhal creatures take extra damage from Radiant damage, as shown in their stat blocks.
The Lamp Cleanse spell removes 1 Exhaustion level gained from Vhal exposure, in addition to its normal effect.
A bright lamp keeps a weak site from harming a creature. A creature in Bright Light from a lamp or a spell in a Weak site makes no exposure saves.