Umbral Mists

The Worldfast separates Mangal from other planes, but a limited portion of the transitional planes of the Border Ethereal and Astral Plane remain connected, like a thin film overlaying the material world of Mangal.  The properties of these planes have melded together over the millennia, forming what denizens of Mangal know as the Umbral Mists (or simply "the Mists"), a hazy mirror to the material world of Mangal.   Within the Umbral Mists, thought and spirit mingle with fey spirits and reclusive fiends.  Most regions of the Mists appear as a gray, shadowy version of the material world as if perceived through a thick, swirling fog.  Many of the beings that dwell primarily in the Umbral Mists distort their domains, shaping them to their liking (or occasionally betraying their true nature).  Some beings also create pocket dimensions within the Mists, though most are not more than a few miles in diameter.  

Role of the Umbral Mists

The Umbral Mists allow many spells and effects to function within Mangal without severely altering the core spell and ability mechanics of Dungeons and Dragons.  Spells that teleport, conjure, make creatures invisible, or interact with the Astral or Ethereal Planes in other ways simply make use of the Umbral Mists on Mangal.  Similarly, spells or effects that interact with the Feywild or Shadowfell can be ruled to interact with the Mists at your Dungeon Master's discretion.   Note that while the Mists fill the role of these transitory dimensions, it is distinct from them.  For example, the Raven Queen is a specific character native to the Shadowfell; her domain would not necessarily exist within the Umbral Mists.  More general effects usually tied to the Shadowfell, like shadow magic, could be accessed through the Mists.