One of the most prevalent elements of Shadow World is the connection between Kulthea and the “Pales” and other dimensions. The Ka’ti’viir discovered these realms later in the First Era, brought “Demons” and other denizens to Kulthea for study and experimentation and the devastation wrought at the end of the First Era, created rifts and portals that increased the incursions of Demons into the Shadow World.
The Master Atlas mentions “Demons” 153 times (Lugroki are only mentioned 43 times) and they appear to be the default adversary in Shadow World and at the middle of most of the major conflicts, including the Wars of Dominion.
The continual presence of Demons throughout Kulthea is one of the reasons I modified the various Demonology lists in BASiL. In my lists, Demons must be actively sent back (banishments) or sent back through an open gate. They don’t simply disappear at the spell duration. So while many Demons arrive to Kulthea through Gates, Rifts and other Essaence phenomena, some others are Demons brought through various summoning spells.
If you think about it, the story of Kulthea is one of other dimensions. The Shadow World is a crossroads for a variety of dimensional beings; a Skinwalker Ranch” of the universe! The true antagonists of Shadow World are Demons, Dark Gods, Agothu and the Unlife–it’s not really the story of Orcs, Goblins and Trolls; and really not even Dragons.
If you utilize the Pales in your campaign, you should check out the Book of Pales, that I posted on the RMForums. It’s really just the beginning of a book; I have outlined NPCs, major figures, more creatures, more Demons and some adventure ideas in the hopes that it could be published some day. But it’s a start and hopefully contains some useful ideas for introducing the Pales to your players.