Ascendants Rising - A Forgotten Realms Campaign
While Zekknar learned much of the Shadowfell while training to be a Mage in Myth Drannor, and Thunt knew something of the plane of darkness while learning the ways of his goddess, Chauntea; most of the detailed knowledge (below) came from the books you seized when upon defeating Bairwin Wildarson, head priest of the Cult of Shar in Winterhaven.
A gloomy echo of Toril, the Shadowfell is at once ancient and new. The dark goddess Shar reshaped what was then known as the Plane of Shadow during the years of chaos following the Spellplague. In her craft, she folded in the energy of death that didn’t make the transition to the Elemental Chaos. She renamed her creation the Shadowfell, which became its common name among mortals, though some still refer to it simply as “Shadow.”
The Shadowfell is a dim, eerie place. Where the Feywild reflects the world in breathtaking ways, the Shadowfell reveals a decaying, nightmare landscape of dull colors. A brooding half-light replaces the Feywild’s fanciful twilight, and every feature of the place seems macabre and threatening. Fields of necrotic energy, usually too weak to do more than unnerve the living, wander across the baleful shadowscape.
Crossing into the Shadowfell is harder than crossing to the Feywild. Merely stumbling into Shadow is fairly uncommon. Still, places within the world connect to the Shadowfell through a thin veil. These portals are easy to spot and are common in the deep Underdark, miles below the surface.
Native creatures stalk travelers here. So do the restless dead, the souls of those who pass into Shadow but refuse to move on. Humanoids of the Shadowfell are at least as bad as fey. Worse still, creatures that serve Shar, Sseth, Talona, and Orcus make their way into the Shadowfell for various nefarious purposes. True safety is hard to come by in these dark lands.