This section describes a few examples of particularly unusual hazards that adventurers might encounter on their adventures.
The hazards presented here can be potentially identified with a successful Intelligence (Arcana), Intelligence (Nature), or Intelligence (Religion) check, depending on the circumstances. Use the guidelines in d20 Test Section to set an appropriate DC for any check made to spot or recognize a hazard.
Brown mold feeds on warmth, drawing heat from anything around it. A patch of brown mold typically covers a 10-foot square, and the temperature within 30 feet of it is always frigid.
When a creature moves to within 5 feet of the mold for the first time on a turn or starts its turn there, it must make a DC 12 Constitution saving throw, taking 22 (4d10) cold damage on a failed save, or half as much damage on a successful one.
Brown mold is immune to fire, and any source of fire brought within 5 feet of a patch causes it to instantly expand outward in the direction of the fire, covering a 10-foot-square area (with the source of the fire at the center of that area). A patch of brown mold exposed to an effect that deals cold damage is instantly destroyed.
Some cemeteries and catacombs are imbued with the unseen traces of ancient evil. An area of desecrated ground can be any size, and a Detect Evil and Good spell cast within range reveals its presence.
Undead standing on desecrated ground have advantage on all saving throws.
A vial of holy water purifies a 10-foot-square area of desecrated ground when sprinkled on it, and a Hallow spell purifies desecrated ground within its area.
This acidic slime devours flesh, organic material, and metal on contact. Bright green, wet, and sticky, it clings to walls, floors, and ceilings in patches.
A patch of green slime covers a 5-foot square, has blindsight out to a range of 30 feet, and drops from walls and ceilings when it detects movement below it. Beyond that, it has no ability to move. A creature aware of the slime's presence can avoid being struck by it with a successful DC 10 Dexterity saving throw. Otherwise, the slime can't be avoided as it drops.
A creature that comes into contact with green slime takes 5 (1d10) acid damage. The creature takes the damage again at the start of each of its turns until the slime is scraped off or destroyed. Against wood or metal, green slime deals 11 (2d10) acid damage each round, and any nonmagical wood or metal weapon or tool used to scrape off the slime is effectively destroyed.
Sunlight, any effect that cures disease, and any effect that deals cold, fire, or radiant damage destroys a patch of green slime.
Few know for sure where russet mold came from. One historical account tells of adventurers in a mountain range discovering russet mold and vegepygmies in a peculiar metal dungeon full of strange life. Another story says that explorers found russet mold in a crater left by a falling star, with vegepygmies infesting the forest nearby.
The mold is found only in places that are dark, warm, and wet. Russet mold that spreads out across a metal object can be mistaken for rust, and a successful DC 15 Intelligence (Nature) or Wisdom (Survival) check is required to identify it.
Any creature that comes within 5 feet of russet mold must make a DC 13 Constitution saving throw as the mold emits a puff of spores. On a failed save, the creature is poisoned. While poisoned in this way, the creature takes 7 (2d6) poison damage at the start of each of its turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Any magic that neutralizes poison or cures disease kills the infestation. A creature reduced to 0 hit points by the mold dies. If the dead creature is a Beast, a Giant, or a Humanoid, one or more vegepygmies emerge from its body 24 hours later: one from a Small corpse, two from a Medium corpse, four from a Large corpse, eight from a Huge corpse, or sixteen from a Gargantuan corpse.
Russet mold can be hard to kill, since weapons and most types of damage do it no harm. Effects that deal acid, necrotic, or radiant damage kill 1 square foot of russet mold per 1 damage dealt. A pound of salt, a gallon of alcohol, or magic that cures disease kills russet mold in a square area that is 10 feet on a side. Sunlight kills any russet mold in the light's area.
Yellow mold grows in dark places, and one patch covers a 5-foot square. If touched, the mold ejects a cloud of spores that fills a 10-foot cube originating from the mold. Any creature in the area must succeed on a DC 15 Constitution saving throw or take 11 (2d10) poison damage and become poisoned for 1 minute. While poisoned in this way, the creature takes 5 (1d10) poison damage at the start of each of its turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a successful save.
Sunlight or any amount of fire damage instantly destroys one patch of yellow mold.