The constant smog in Gracklstugh causes grackle-lung in living, breathing creatures, resulting in persistent, wracking coughs and the spewing of thick, black phlegm. Whenever a living, breathing creature finishes a long rest in Gracklstugh, it must make a DC 11 Constitution saving throw. On each failed save, the creature gains one level of exhaustion as its airways become increasingly clogged. A creature that reaches level 6 exhaustion dies, as normal.
A creature with one or more levels of exhaustion brought on by grackle-lung must succeed on a Constitution check to take the Dash action. If the check fails, the action cannot be attempted. If the creature attempts to cast a spell with a verbal component, it must succeed on a Constitution check or be unable to complete the spell, causing the spell to fail with no effect. The DC for each check is 10 + the creature's current exhaustion level.
If a creature's exhaustion level drops below 1, it no longer suffers the effects of grackle-lung and becomes immune to it for the next week. Duergar and derro are inured to grackle-lung, making Constitution checks against it with advantage. Any spell or effect that cures disease also cures grackle-lung, effectively removing all levels of exhaustion brought on by the affliction.