Paul Farquhar
Legend
NWN2 Masks of the Betrayer has a shadow plane that is a dark parallel of the real world.
You mean impossible to map out exactly...The nature of the Feywild and the Shadowfell makes them "interesting" to map out exactly.
Another adventure to look at is 3e Cormyr: Tearing of the Weave which includes a trip to the Shadowfell "echo" of one part of the kingdom. The comparison between Material Plane and Shadow Plane will help you build your own maps.
The Shadowfell was a 4E evolution of the (Demi)Plane of Shadow. If there was theft, 4E designers stole from Ravenloft and the Demiplane of Shadow. They incorporated it into the 4E lore, but so does every setting now as it is core design for the game.Only the Plane of Shadow is not the same thing as the Shadowfell (except where, of course, the FR have tried to steal everything cool that ever existed outside of them and tried to integrate it in a horrendous mish-mash that is not only inconsistent with itself, but also devoid of anything original and with personality). The Shadowfell is, IMHO, much more interesting than the Plane of Shadow ever was, although it was already a favourite plane of ours in AD&D.
The Shadowfell was a 4E evolution of the (Demi)Plane of Shadow. If there was theft, 4E designers stole from Ravenloft and the Demiplane of Shadow.
They incorporated it into the 4E lore, but so does every setting now as it is core design for the game.
Th mentioned 3E module is likely a major influence in that 4E decision. The adventures enter a Demiplane of Shadow location that is a dark mirror of the Material Plane. The module came out a year before 4E, IIRC.