From ‘Introduction to the Planes,’ by T. Ketzvih:
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The mortal realms are, unsurprisingly, the most hospitable realms to mortal life within the entire cosmos. While many planes- and even realms in total- can be inhabited by mortals, it is the mortal realms from which all mortals come from, and there wherein they most feel at home. Rare, are the Voids large enough to swallow an entire world. Rare, is the fire which threatens to wipe out all life upon a continent. Here, all life can flourish freely, and mortal magic is at its most potent. Perhaps such is something of a disingenuous claim, given mortal magics are often made with the Mortal Realms in mind, but it is certainly the cradle of the most diverse sorcerous effects across the cosmos.
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Material
The Material realms- in particular the Prime Material, are where I (and presumably you) make our homes. It has the most pleasing balance of all the realms, where magic functions as it ought; all elements may be found in good (though rarely equal) proportion. The air is breathable to mortals, the ground will not give way in most places, and countless continents serve as islands within an eternal sea- or perhaps an enormous lake is surrounded by land, who can truly say?
The Material planes are true planes, and stretch infinitely in all directions. This does indeed mean it is impossible to reach the edge of the world traveling by land or sea, and flying up or digging down will not lead to either the Divine or Elemental realms respectively, despite common legend. Instead, should you progress far enough, you will instead find another sky-island, or a cavern large enough to hold a world, or an ocean so vast it is impossible to fathom.
The Material Realm’s most interesting feature from a realmistry perspective is that it has the most Slips of all the realms. While nearly all Planes possess them in some frequency, only the Material Realm possesses true Slips in such quantity and with such frequency that it does seem that everything emits mana constantly. Should you kindle a flame within even Faerie, it will not gush forth fire mana. Water will not trickle forth mana of its own nature within the Darkrealms. And of course, mana does not behave anywhere close to the same way in the Ethereal, so it is meaningless to compare it thusly.
But it is due to this feature which brings some of the strongest ley lines in the cosmos to the forefront in the Material. While the Elemental Realms have their own currents and eddies, and the Divine possess their tides of power, only in the Material will you find such massive and coursing, immaterial veins of magic rushing across the landscape, combining in strange and wonderful ways where they meet.
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Darkrealms
The Darkrealms are usually thought of as an echo between the Material and the Elemental Realm of Shadow, but to do so is to render it a disservice. While it does indeed bear superficial similarities to Shadow, predominantly due to the perpetual late twilight, eternal eclipses casting long and deep shadows across much of the realm, or simply due to massive barely-lit caverns occupying much of a given plane, it is important to note that everything within the Darkrealms is material. It will not bend and warp with the lightest touch of magic, and is indeed in many ways quite the opposite. The Darkrealms are some of the most impervious to external manipulation of all the realms.
Scholars disagree on why this is, but some speculate that it is due to the Shadow-like nature of the realm absorbing and vanishing magic and other energies with barely a trace. As evidence, they point to the generally oppressive nature of the plane towards magic, and how even the simplest of spells can prove substantially harder to cast and significantly more tiring to maintain once it has been created. A basic light spell normally castable by a fourth year apprentice requires a sixth-year initiate instead, and similar increases in difficulty can be observed regardless of the type of spell being used.
Others think that it is a shadow of another realm- be it the Material or another- and attempting to change the landscape while only interacting with a shadow is foolishness. As evidence, they point out how even once disturbed, the world of Shadow may slowly reset itself to a given state entirely under its own volition even when successfully changed, and how many planes of the Darkrealms bear a striking resemblance to the geography of other planes Mortal, Divine, and even Primordial alike. Similarly, Slips to the Darkrealms are especially common across the cosmos, and it is fairly easy to stumble into the realm through an unnaturally deep shadow.
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Yet others believe all who enter the Darkrealms become less real themselves while they are within, as evidenced by the effects it can have on those who live there for generations. The darkness seems to permeate their very soul, and they become darker versions of themselves. In time, all species who live within the realm become little more than wisps of shadow, parasites able to latch upon interlopers not cautious to protect themselves.
Regardless of the reason, affecting anything within the Darkrealms can be rather difficult. Not only are many of the inhabitants strange, dark-filled creatures who feast upon life while not seeming truly alive themselves, but the realm itself seems to interfere with magics. Neophyte mages find their magic all but impossible to call upon, archmages find their repertoire substantially harder to call upon, and even experienced planar travelers
Yet for all its dangers, the Darkrealms have their immense uses. In nearly every shadow, the Darkrealms twist into a sub-plane, but between those and the relatively low population density for the mortal planes, the Darkrealms are often considered host to the greatest locale in the cosmos for hiding something important or trivial. However, this comes with its own price. Due to how common Slips to the realm are, it is certainly possible for the greatest hidden treasure to mysteriously appear on a plane halfway across the cosmos, having fallen through a temporary Slip to distant lands. This is still phenomenally rare, and many still view the chance as insignificant enough to warrant its use, but in time all which is hidden in the dark will come to light.
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Ethereal
Many of the Ethereal realms do not properly exist as their own separate layers of reality, but are instead overlaid upon other parts of the mortal realms, simply different. Venturing into the Ethereal from the Material often results in being within the same space, but different in some way. Perhaps walls become translucent and insubstantial, objects become more metaphor than real, and people become more defined by their power of will and magical aptitude than their actual bodies. Perhaps all is the same, other than being perfectly mirrored. Perhaps it is a portion of reality which can be warped and manipulated easier than true Material, lending itself to fantastic displays of warping the fabric of space around the interloper.
It is possible to learn much while within the shallow Ethereal, capable of observing the Material while being all but invisible to it in turn. This, alongside the short-distance traversal abilities which can be gained from dipping temporarily into an appropriate plane, are the primary use of this realm.
However, the Ethereal is substantially more than simply the shallowest planes. The further from the Material that you venture, the more the mind holds sway. While similar to the Astral in some ways, where it is thought which holds strength, the Ethereal is far more chaotic, and closer to a waking dreamland, a psychedelic axis of reality where anything is possible. A stray thought can rip through the plane like a storm, scattering all in its wake. Literal nightmares are just as real, just as physical as the strongest spell, but so too are the grandest daydreams. It is both wonderful and horrifying, and can change which is most prevalent within the span of a single thought.
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Faerie
Faerie is certainly the oddest realms which readers of this book are likely to visit, and is in many ways impossible to properly prepare anyone for. The realm itself cares little for rules except insofar as how best to change them unexpectedly for any visitors. Night may fall with the rising of the sun, winter may arrive as an army doing battle with the summer, climbing up a tree may result in becoming stuck within its roots, and walking backwards leads to different places than walking forwards might- and it may well change from moment to moment which orientation leads in what direction.
While belief that planes are sapient or sentient may have fallen off as scholarship on the subject has progressed, Faerie is one of the few realms wherein belief that at least several of its planes are aware. This is due in part to the nature of godhood within the realm. While grasping divinity is far simpler on it than almost anywhere else in the cosmos, to do so is to become one with the Realm in a very unusual way. Its proclivities, and that of all other deities upon the plane, overlap and coalesce into a crude form of awakening.
This pseudo-gestalt divinity manifests in a unique way upon each plane, and means that while less sensitive to change than the Ethereal, Faerie is no less strange and bizarre. While many of the planes bear a substantial resemblance to the Material, but far more lush with life and positively brimming with magic, others are all but incomprehensible to mortals.
Planes where directions are measured in hard and soft, where seasons are armies at war with one another, where a simple name can make the difference between life and death, where beauty is traded for talent and magic is sold for the color of one’s hair. All of those and yet stranger still can be found within Faerie.
Magic is ubiquitous within the Realm. While Material realm magic is still technically unreliable, the plane itself is susceptible to strong enough belief. Thus, a well-practiced spell may do as much or more than it had ever managed before, and simply anticipating an event which ought to happen can often be sufficient to cause it to occur in reality as well. Or, in some particularly contrary planes of Faerie, its opposite.
While I rarely discuss the inhabitants of the realms in this introductory section, the denizens of Faerie must be prepared for before any interaction occurs. Approaching them unprepared is all but worse than even a death sentence, but proper preparation can yield substantial rewards. Above all, be careful when dealing with Fey.