Valthrun's Book on the Shadowfell
An untitled treatise on the Shadowfell
The shadowmist is a phenomenon whose true origin is a mystery. Often it appears in those places where the barrier between our world and the Shadowfell is thin. Others view it as a manifestation of the Raven Queen’s will. Scholars are torn about the difference in the nature of the shadowmist with that of a shadow crossing. The latter, however, appears in fixed places, though it may only be open on certain occasions. Shadowmist appearances, however, cannot be predicted.
Whatever its true nature, once the shadowmist has spread significantly, it transports those within it into the Shadowfell.