A friendly bronze dragon keeps a watchful eye on a storm-tossed ship.
Characters crossing a frigid tundra might suffer the effects of extreme cold, while a visit to a cloud giant’s castle might subject characters to the effects of high altitude. The following sections provide rules for handling these and other environmental effects.
A dead magic zone is an area where the fabric of magic is torn. The effect is the same as the Antimagic Field spell, except that it is permanent and typically covers an area no more than 300 feet in diameter.
Swimming through deep water (more than 100 feet deep) presents additional challenges because of the water’s pressure and cold temperature. After each hour of swimming in deep water, a creature that lacks a Swim Speed must succeed on a DC 10 Constitution saving throw or gain 1 Exhaustion level.
When the temperature is 0 degrees Fahrenheit or lower, a creature exposed to the extreme cold must succeed on a DC 10 Constitution saving throw at the end of each hour or gain 1 Exhaustion level. Creatures that have Resistance or Immunity to Cold damage automatically succeed on the save.
When the temperature is 100 degrees Fahrenheit or higher, a creature exposed to the extreme heat and without access to drinkable water must succeed on a Constitution saving throw at the end of each hour or gain 1 Exhaustion level. The DC is 5 for the first hour and increases by 1 for each additional hour. Creatures wearing Medium or Heavy armor have Disadvantage on the save. Creatures that have Resistance or Immunity to Fire damage automatically succeed on the save.
A creature can be immersed in frigid water for a number of minutes equal to its Constitution score before suffering any ill effects. Each additional minute spent in frigid water requires the creature to succeed on a DC 10 Constitution saving throw or gain 1 Exhaustion level. Creatures with Resistance or Immunity to Cold damage automatically succeed on the save, as do creatures that are naturally adapted to living in ice-cold water.
Traveling at altitudes of 10,000 feet or higher above sea level is taxing for most creatures because of the reduced amount of oxygen in the air. Each hour such a creature spends traveling at high altitude counts as 2 hours for the purpose of determining how long that creature can travel (see “Travel Pace” in chapter 2).
Creatures can become acclimated to a high altitude by spending 30 days or more at this elevation. Creatures can’t become acclimated to elevations above 20,000 feet unless they are native to such environments.
Certain planes of existence—and areas on the Material Plane affected by them—have supernatural effects on creatures within them. Several examples are presented below. See chapter 6 for more information about the planes of existence.
The plane of Acheron rewards a creature for harming other creatures by imbuing it with the strength to keep fighting. While in Acheron or a region under its influence, a creature gains Temporary Hit Points equal to half its Hit Point maximum whenever it reduces another creature to 0 Hit Points.
On the plane of Arcadia and in regions where its influence is felt, creatures benefit from supernatural vitality, which grants them Immunity to the Frightened and Poisoned conditions.
On the plane of Mount Celestia and in regions where its influence is felt, creatures are blessed by the pervasive beneficence of the plane. Creatures other than Fiends and Undead gain the benefit of the Bless spell as long as they remain in an area of blessed beneficence. In addition, such a creature that finishes a Long Rest in the area gains the benefit of a Lesser Restoration spell.
On the plane of Gehenna and in regions where its influence is felt, creatures are driven to loathe helping one another. Whenever a creature subject to Gehennan cruelty casts a spell that restores Hit Points or removes a condition other than Invisible, the caster must succeed on a DC 10 Charisma saving throw, or the spell fails and is wasted.
The winds of Pandemonium are common in Pandemonium and regions where its influence is felt, including parts of the Underdark. A creature makes a DC 10 Wisdom saving throw after each hour spent among the howling winds. On a failed save, the creature gains 1 Exhaustion level. The winds can’t increase a creature’s Exhaustion level above 3. Finishing a Long Rest doesn’t reduce a creature’s Exhaustion level unless the creature can somehow escape the winds.
Slippery ice is Difficult Terrain. A creature that moves onto slippery ice for the first time on a turn or starts its turn there must succeed on a DC 10 Dexterity saving throw or have the Prone condition.
Strong wind imposes Disadvantage on ranged attack rolls with weapons. It also extinguishes open flames and disperses fog. A flying creature in a strong wind must land at the end of its turn or fall.
A strong wind in a desert can create a sandstorm that imposes Disadvantage on Wisdom (Perception) checks.
Thin ice has a weight tolerance of 3d10 × 10 pounds per 10-foot-square area. Whenever the total weight on an area of thin ice exceeds its tolerance, the ice in that area breaks. All creatures on broken ice fall through. Below the ice is frigid water (see “Frigid Water” above).
A past magical disaster or uncontrolled surge of power in a particular place can cause the fabric of magic to unravel, creating a wild magic zone. In such an area, which is typically no more than 300 feet in diameter, magic behaves unpredictably.
Whenever a creature expends a spell slot to cast a spell in a wild magic zone, roll 1d20. If you roll a 20 on the die, roll on the Wild Magic Surge table in the Player’s Handbook to create a magical effect.