[RPG] What monsters and races are from the Shadowfell

Here are some links about the Wall of the Faithless: NWN2 Wiki and FR Wiki

I've read a lot of game books and novels set in the FR, but not much is mentioned about the WotF. The only place where it plays a major role is the game expansion Neverwinter Nights 2: Mask of the Betrayer

While the general section on beholders in Lords of Madness doesn't give any particulars of the furniture in the beholder's lair, there is an example lair detailed later in the chapter (page 56). I won't reproduce the whole thing here, but the important room for our purposes is the beholder's personal chamber:

This large chamber is quite impressive; the walls and ceiling are covered with intricate carvings depicting beholders eating humanoids, and vast fields of mushrooms with writhing tendrils. On the ceiling above, the image of a single immense beholder watches everything. Two large, uneven stalagmites protrude from the floor along the northeastern wall, and to the south stand several well-made statues of powerful-looking adventurers and fearsome monsters. In the center of the room sit numerous desks, each of which is covered with mounds of papers and books.

This chamber is Sekarvu’s personal lair, and where it spends the majority of its time.

There is no mention of a bed, or indeed any furniture beyond the desks. So either the beholder sleeps on a desk (face it, we all have occasionally), or it continues to levitate while it sleeps.

A possible source of further details on beholders would be the AD&D 2e book I, Tyrant, which was the book in the Monstrous Arcana series dedicated purely to beholders.