Shadowfell (Stormforge Supplement)
From D&D Wiki
The Shadowfell; also called the Plane of Shadow, sits below Aerinthia like a pale and ruined reflection. The darkness of the Negative Energy Plane leeches the planar essence from the Shadowfell and breaks through to Aerinthia in the dark and shadow places of the world.
Like the Aerinthian Feywild, where the Shadowfell touches upon Aerinthia it changes the world. Across Neveril the Shadowfell only touches the continent of Aerinthia. Beyond the Storm the connection has been severed. Also the Shadowfell only has a tenuous grasp in many parts of Aerinthia, like Kadishmar, the Meadowlands, Stormguard, and the Shieldlands.
It is unknown how the Shadowfell is affected throughout the rest of Stormforge.