A deadly fog surrounds the land of Barovia and engulfs any creature that tries to leave. Even flying creatures are subject to the fog's effects, which are as follows:
A creature that starts its turn in the fog must succeed on a DC 20 Constitution saving throw or gain one level of exhaustion. This exhaustion can't be removed while the creature is in the fog.
No matter how far a creature travels in the fog, or in which direction it goes, it gets turned around so that it eventually finds itself back in Barovia.
The area within the fog is heavily obscured (see Vision and Light).