Sigil is a city that exists on many levels, and casts its reflections into other realities that exist parallel to the Material Sigil. They resemble the reality of other planes (all transitive planes) but they aren’t parts of these planes. An Ethereal or Shadow Sigil is not at all connected to the Ethereal or Shadow Plane. Instead they are reflections of Sigil, co-existing with the material form of Sigil.
Sigil's Ethereal Reflection
While Sigil is misty and foggy enough, it is even more so over here. The strangeness on this reflection of Sigil is even stranger for it is home to many races beyond the standard sampling of the material Sigil's population. Some are foreign and completely alien; others have been long dead for years. In fact a sizable number of Sigil's undead live here as opposed to places in the Material Sigil such as the Mortuary and The Drowned Nations. Ghosts of Sigil's past live here; some could recall some of the earliest factions that lived there.
The streets and buildings here generally mirror that of the Material Sigil, however there are still some differences. Rooms and tunnels that did not exist in the Material Sigil exist here. And some large ancient buildings that don't exist elsewhere can be found here.
The Dabus that live in this part of Sigil roam the streets shaping the protomatter of this plane to maintain the streets. It's thought in that the mysterious place from where the Dabus come from and go to is located somewhere on this plane, but no one every knows. It's thought that there is in fact a city belonging all to the Dabus that exist here. But everyone who has went to find it has never come back.
Also of interest to this part of Sigil are the mazes which are demiplanes connected to this reflection, where enemies of the Lady of Pain find themselves.
Sigil's Shadow Reflection
This is a dark and bleak reflection of Sigil where the "sky" never becomes bright. Peak is only slightly brighter than anti peak is. Many unknown races live here. And it's thought that the Revolutionary League has plenty of secret safehouses in this most dangerous region of Sigil.
The streets and landscapes of Shadow Sigil only mirror the most familiar appearances and layout of Sigil. Its physical features may shift from time to time unpredictably. Any many ways Shadow Sigil is a warped reflection of Sigil with dark overtones. There are ancient long lost communities and intimidating huge citadels found here which can't be found in the other Sigils.
The Dabus of this part of Sigil are darker and more sinister in appearance. They move quickly and silently going about their business. Here they have the ability to shape Shadow stuff to their will bringing about whatever changes they want here. There are also rumours that Sigil's Shadow is in fact the very place that the Lady of Pain herself resides in, though no one is willing to prove that.
Entities known as the Voices of the Black Void have been known to lure people to parts unknown in this reflection. Their agenda is unknown, but those they’ve lured into their influence are never the same again, if they ever return.
Sigil's Dream Reflection
Depending on which cosmology is used and how the Plane of Dreams work such as the Plane being a transitive plane as written in Dragon or at least features of that, determines whether this option is valid or not.
Sigil's Dream Reflection has the least in common with Sigil's other counterparts. There are some vague similarities to the Material Sigil here. The landscape is all varied and different here, in many ways the environment is in conflict with itself as one part of this plane is very alien to another part neighbouring it. It's said that a piece of every world on every plane exists here as places such as cities buried under sand neighbour pyramids in snowy wastelands.
If there's one thing to be said about Sigilians it's that their dreams are extremely varied and unpredictable. The effect over here can be catastrophic, making this one of the most dangerous counterparts of Sigil. The inhabitants of this part secretly travel from dreamscape to dreamscape living off the dreams of all Sigilians. A Dreamheart also exists here, lying within the centre of Sigil's ring, it holds an important secret to the Cage, but none have discovered it yet.
The Dabus can also be found here, it's thought that their job here is to ensure that the dreams of Sigil can be safely maintained and used for construction parts in other reflections. The words of the Dabus are much easier to comprehend here.
Sigil’s Faerie Reflection
The Plane of the Faerie itself is an anomaly, an Outer Plane that is coexistant with some other worlds. The plane is constantly shifting in its position among the planes, as the home of both the Seelie and Unseelie Court.
In Sigil there is a "beach head" or reflection of the Faerie Plane that exists here, cut off from the rest of the plane. Faeries and others roam here in a world that looks quite similar to the Material Sigil; however various parts of this reflection are shared with parts of the Spirit, Dream, Ethereal and Shadow reflections. Stepping in certain parts of the Faerie reflection will dump one into any of these other reflections.
Sigil's Spirit Reflection
If the Spirit World exists, then in Sigil its reflection resembles its material counterpart except that its features and structures are more intense and exaggerated. In the Spirit Sigil the many spirits of Sigil's people, building and streets live alongside many different beings. The Godsmen, their successors the Mind's Eye, the Sensates and the Ciphers all have an interest in this part.
Like many of its other counterparts, there are places here that don't exist in others. Entire neighbourhoods based around particular concepts exist around here. And powerful spirits here have the ability to affect changes in the physical Sigil, such as destroying and creating buildings, alleyways and streets. However even they are wary of the Lady of Pain, thought by many to have originated from this reflection.
The Dabus of Spirit Sigil are spirits themselves, often working together with their physical counterparts, shaping the spiritual reflection of Sigil before it's physical part.
I'm confused, according to the Planar Handbook, Sigil (like all the Outer Planes) has no connection to the Ethereal Plane. But if there was an Ethereal Sigil that was separate from the Ethereal Plane, would the various spells that require the Ethereal Plane now work in Sigil?
Without spells like "etherealness" the only way to access Ethereal Sigil would be through portals.
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