The Aether is the expanse of nothingness that separates the remaining shards of the Inner Planes. It is dangerous to fall overboard and lose the protection of a ship's atmosphere field. Doing so is very much like plunging beneath the waves of near-freezing temperature ocean water.

While beings exposed to the airless cold of the Aether are not immediately doomed, they are in great danger. A character outside an atmosphere field can hold their breath for 1 minute plus 1 additional minute for each point of Constitution bonus. After this time they will fall unconscious, their hit points fall to 0, and they begin making death saving throws. If they become stable and they are still in space they can’t remain stable. Instead they must start making death saving throws again. This continues until they die unless they are saved in some way. However, they will probably die from the cold before they suffocate to death.

The extreme cold requires characters to succeed on a DC 10 Constitution saving throw each round or receive 1d4 points of cold damage, or 1d6 points of cold damage if wearing metal armor. Additionally, for every three failed saves they gain one level of exhaustion. Creatures with resistance or immunity to cold damage automatically succeed on the saving throw. Wearing cold weather gear (thick coats, gloves, and the like) gives you advantage on the first 10 saving throws only.

Creatures that can survive in the Aether like dragons are able to propel themselves through the Aether by flying or swimming. Player characters may move themselves through the Aether at a quarter of their movement value, or they can continue their momentum by getting a running start on a nearby gravity plane and drift.