Shadow/Mirror Plane
The Shadow (or Negative) Plane and the Mirror (or Inverse) Plane are the least understood plane(s) of existence. Not only are their very nature difficult to understand, what makes them more confusing is that they are not two dimension or halves of a dimension, but different names and perspectives of the very same realm.
The Shadow (or Negative Plane) is the opposite of the Material Plane and Astral Plane. The Mirror (or Inverse) Plane is the opposite of the Ethereal Plane and Astral Plane. Mathematical theory describes the structure as consisting of one negative dimension of the Material Plane (Shadow), one negative dimension of the Ethereal Plane (Mirror), and one inverse dimension of the Astral Plane. This means that Shadow/Mirror inhabits every point in each of the three other dimensions, but in an "inverse" way. Time exists in the Shadow/Mirror, but "flutters", making movement there seem faster and sporadic relative to the M-E temporal line. ,
Beings from each of the three main planes generally characterize the entire Shadow/Mirror realm as "evil" (even the demons of the Ethereal realm) because there is some aspect to it that appears antithetical and in opposition to life on the other three realms. Interaction with the Shadow or Mirror realm often results in hostility. For this reason, the Shadow/Mirror Plane is often used as a means of capital punishment by beings in the Astral and Ethereal realms. Despite this general sentiment, there are some beings who are either very open-minded or terribly naive to think that entities from the Shadow are just misunderstood because of their negative inverse state.
Traditional coordinate notation for the Shadow Plane is ℎ(-x, -y, -z, δ) and/or Mirror Plane is ℏ(-i, -j, -k, δ) using the appropriate point of reference and dimension transform function. In other words, the Shadow Plane and Mirror Plane are the same plane, but depending on whether you enter from the Material Plane or the Ethereal Plane, the results may seem very different based on your original point of view. That is to say, two people could be at the exact same location, and yet experience and sense two completely different experiences depending on how they entered this plane of existence. It really does boggle the mind.
Comments
Author's Notes
Q: Is this like the "Upside Down" or similar dimension one might see in the series, Stranger Things?
A: I suppose it could be experienced as such, but I promise that this general concept is legally distinct and in no way is meant to duplicate that franchise.