Plane of Shadow
The Plane of Shadow was a shadowy Transitive Plane that overlapped both the Material Plane and the Ethereal Plane. It was utterly devoid of life, and due to its morphic nature could be used to travel great distances quickly. Many unique species (such as the shadar-kai) made their home in this plane. As a result of Kiaransalee's attempt to breach the magical barrier around Doth'Mordun, the Negative Energy Plane drained into and merged with the Plane of Shadow, creating the Shadowfell.