Negative Energy Plane
The Bottom of the Multiverse. The Cold Land. The Great Void. The Nothing. Death.
The Plane of Negative Energy holds many names, each accurate in its own way. Where the Positive Energy Plane is the wellspring from which all life comes, this is the pit into which it drains. Where Positive brings order, Negative brings disorder. Where Positive brings creation, Negative brings dissolution. This space is a threat to all that lives, and a paradise to all that does not.
Like each of the inner planes, the nature of the Negative Energy Plane is essentially defined by the energy that suffuses and comprises it. Obviously, there are no native living beings here in the traditional sense, though this isn't to say the plane is empty. It has its own ecosystem of a sort, though it's a cold, unchanging one. There are living beings of a sort, an interest and a mystery to planar biologists for ages. From the microscopic organisms that inflict sickness and rot across the multiverse, to the very basic blackball and trilloch, to the ever-curious xeg-yi, up to the nightshade — considered the apex predator of Negative. Even some otherwise-mortal beings have somehow managed to adapt to the plane over ages of exposure without death; while lifeless in a strict sense, the plane is far from inactive in the sense of, say, Vacuum.
Undead often find themselves gravitating to this plane as well, their very existence fueled by the substance that makes them up; and unlike living beings within Positive, undead are at no thread of overload here, for their physical substance is already essentially saturated with the Negative in a way very dissimilar to the Positive that allows for life; where living beings generate and respond to positive, undead are simply driven by it and can only hold so much within their forms before no further will enter. From mindless skeletons and zombies called here by instincts they can't comprehend all the way to demiliches seeking to better understand the nature of death, undead of all varieties can and have made their way here, and even in places established settlements of a sort; Deathheart (née Heart of the Void), a former mortal colony since occupied by the undead, is an illustrative example of such.
Unfortunately, living beings are not so protected. Indeed, life is utterly anathema on Negative, and is quickly snuffed out by the energies of the plane.  Further, obviously, there is no air upon the plane, nor light; any travelers must bring their own, though they'll find lighting their way difficult here. All this can likely be assumed by most, but the effects of such massive concentrations of negative energy are less commonly known, encountered so rarely outside this plane as such concentrations are. All senses are dulled in Negative, not merely sight: sound is muffled, scent and taste are nearly absent, and touch feels as though a person is a bit numb. Finally, there's always a dull chill upon the plane as well; not enough to freeze, or even injure on its own, but enough that a person can never seem to feel warm no matter what efforts they take. And of course, nonliving objects aren't immune from the entropic effects of Negative, eventually crumbling to nothing if not protected. Movement, at least, is simple; as with most immaterial Inner Planes, motion in the plane is by pure will, directing ones personal gravity as needed to navigate.
Some portions of Negative, naturally, are even worse, the energy of the plane condensing through yet-unknown processes into seemingly-solid "matter". Thus the formation of voidstones, somehow visible in a way even against the darkness of the plane as an utter sinkhole of light. These objects are akin to natural spheres of annihilation (and in fact are a key to their creation), though not quite as deadly. However, they're also more dangerous in that they do not have woven into them the enchantments that allow for control, instead simply drifting by the currents of energy within Negative. In some regions they seem to congregate in vast patches, and most are wise enough to avoid such areas even among natives, for even locals would find themselves destroyed by such pure, concentrated entropy.
Of course, some portions aren't quite as suffused with negative energy as others; though not livable, they're at least easier for a being to combat. In such places (most commonly known as "doldrums") life can get by slightly better. Senses aren't quite as dull, light glows a little brighter, and the plane doesn't sap at a person quite as much. It's in such places that mortals with some desire to live upon Negative will usually make their kip, having to worry less about the plane itself and able to focus more on defending against its inhabitants instead.
Most mortals upon Negative are those that tend towards the sagacious or necromantic, seeking to better understand or wield Negative Energy through direct exposure; few stay for long, of course, instead keeping residence just long enough to accomplish their goals before leaving. Perhaps surprisingly, the Doomguard (though certainly drawn to the core nature of negative energy) tend not to establish any outposts within Negative, approaching no closer than the boundary areas of the negative quasi-planes; to many, the idea of constructing something within Negative is almost sickening. The Dustmen have no such qualms, though, and their Fortress of the Soul is the most well-defended and well-enchanted spot in Negative for the living. Only the most highly-ranked of the faction are allowed to reside within the Fortress, though they aren't entirely cold to travelers looking for a place of safety. Those few outsiders to Negative that find their way are allowed to rest up for a time, but only long enough for the weekly portal to Sigil to cycle, at which point they're quickly ushered through back to the Mortuary and onto the city streets.
Because of the plane's overpowering nature, any spells with any elemental descriptor or the Light descriptor are impeded. Similarly, any spells with the Darkness descriptor are enhanced.
Further, any spells described as using Positive energy (such as cure wounds), are minimized, as are any attempts at channeling positive energy. That is, all variable, numeric effects of such spells are minimized. However, as would be expected, any spells described as using Negative energy (such as inflict wounds), and any attempts at channeling negative energy, are maximized.
- Boundary Regions
- The Vortex (Shiva's realm)
- The plane is Negative-dominant, and any living occupants unprotected against negative energy must make a DC 25 Fortitude save each round or gain a negative level. Further, characters suffer a -10 penalty on any Fortitude saving throws made to regain negative levels while upon the plane. Spells or effects such as death ward or negative energy protection that grant immunity to negative energy negate both effects.
- Any sources of light, mundane or magical, have their illumination dropped by one step, as per the darkness spell; dim light sources can still be seen, but provide no illumination. Further, the range of any light source is cut in half.
- Any unenchanted and otherwise-unprotected objects take 1d6 points of damage a round, doubled for especially positive-aligned substances such as gemstones. They crumble to their basic negative-quasielemental components at 0 hit points. Hardness does not apply to this damage.
- Unlike a sphere, something which touches a voidstone can take a DC 25 Fortitude saving throw to not be destroyed.
- Within a "doldrum", light sources do not have their radius cut in half, though their illumination still declines by one step. Further, living beings (in lieu of taking negative levels) must make a DC 15 Fortitude saving throw each round or suffer 1d6 damage; creatures who die from such exposure crumble to ash, dust, and salt rather than becoming undead. Objects are also less impacted, taking only a single point of damage each round (still doubled for especially positive-aligned substances).
- The Inner Planes, pp.64-67
- Manual of the Planes (3e), pp.80-82
- Planar Handbook, pgs.122-124,185
- Planescape Monstrous Compendium III, pg.12