The Negative Energy Plane

It the blackest night.
It is the heart of darkness.
It is the hunger that devours souls.
The Negative Energy Plane is a barren, empty place, a void without end, and a place of empty, endless night. Worse, it is a needy, greedy plane, sucking the life out of anything that is vulnerable. Heat, fire, and life itself are all drawn into the maw of this plane, which hungers for more. To the observer, there's little to see on the Negative Energy Plane. It is a dark, empty place, an eternal pit where a traveler can fall until the plane itself steals away all light and life. The Negative Energy Plane is the most hostile of the Physical Planes, and the most uncaring and intolerant of life. Only creatures invulnerable to its life-draining energies may survive there, and even they have problems as the negative energy tugs at them imploringly.

Creatures of the Negative Energy Plane

Like its positive energy twin, the Negative Energy Plane is relatively empty. It contains no true elemental forms or versions of Material Plane creatures, and its outsiders are few and far between. Unlike on the Positive Energy Plane, undead thrive in this dark place.
The best-known outsider found on the Negative Energy plane is the xeg-yi. These alien, otherworldly creatures appear to be sentient, though their nature and purpose remain a mystery for many. Outsiders native to the Negative Energy Plane (including the xeg-yi) are immune to the detrimental effects typical of the plane.
The Negative Energy Plane is a hospitable home for the undead, especially undead that drain life energies from their opponents. Wraiths, spectres, and wights are all common, and some powerful vampires and liches make their homes on the Negative Energy Plane as well. The only thing that limits such creatures is the availability of prey, so the undead may be on their way elsewhere when encountered.

Locations and Features of the Negative Energy Plane

The greatest immediate danger on the Negative Energy Plane is the plane itself—its brooding malevolence and soul-sucking nature are a threat to all who cross it. As with its positive twin, there is no air on the Negative Energy Plane. While the environment is not a true vacuum, suffocation is a great peril, and the lack of breathable air tends to keep living creatures away. Similarly, food and drink do not exist naturally on the Negative Energy Plane, so a traveler must bring supplies as well. 
The Negative Energy Plane preys on more than just light. It greedily sucks the energy out of anything that it can. Torches and lanterns last half the normal time. The duration of spells are unaffected, because the nature of the spell itself counteracts the entropic power of negative energy.
Finally, a great danger of the plane is that while it has major negative-dominant and minor negative-dominant areas, the border between the two is indistinguishable. Worse, the border is flexible, and even a stationary traveler may find himself within an energy-draining major negative-dominant area. Spells such as negative energy protection can keep these perils at bay temporarily.
The Negative Energy Plane is completely and totally black. Even if travelers bring their own light source, the inherent power of the plane drains the color from everything, leaving only gray tones lit by flickering light. Clear vision (including darkvision) is limited to 5 feet. Light sources beyond that range appear as indistinct bits of radiance glimmering faintly against the deepest night. Distance is impossible to gauge within this oppressive environment.

Voidstone

In some locations on the Negative Energy Plane, the collapsing intensity of the plane is so great that the negative energy folds in on itself, stabilizing into solid chunks of utterly black matter. These chunks of voidstone might be the building blocks of such items as the sphere of annihilation. Indeed, anything that comes into contact with a voidstone is instantly destroyed. Unlike with a sphere of annihilation, a character touching a piece of voidstone gets a Fortitude saving throw (DC 25) each round he stays in contact with it. Even natives of the Negative Energy Plane are vulnerable to voidstones.
Also unlike a sphere of annihilation, chunks of voidstone cannot be controlled through mental energy. Voidstones may be of any size, ranging from inches across to dozens of feet.

Doldrums

Certain regions on the Negative Energy Plane are less deadly than others, reducing the negative-dominant trait from major to minor or even removing it entirely. These areas, called the doldrums, are relatively static on the plane, so towers, cities, and other structures can be built at their locations.
The perils of such places are twofold. The most obvious threat is the hostile life (and unlife) in the area. A second threat is that the borders of a doldrums area may fail and the deadly tides of negative energy once again wash over the region. Necromancers in particular favor the doldrums for their lairs.

Traits

Subjective Directional Gravity: Similar to the Elemental Plane of Air, on this plane each inhabitant decides his own “down.” 
Normal Time. 
Infinite Size. 
Alterable Morphic. 
Major Negative-Dominant: Each round, those within a Major Negative-dominant plane must make a Fortitude save (DC 25) or gain a negative level. A creature whose negative levels equal its current levels or Hit Dice is slain, becoming a wraith. 
Areas within the plane have only the minor negative-dominant trait, and these islands tend to be inhabited. On minor negative-dominant planes, living creatures take 1d6 points of damage per round. At 0 hit points or less, they crumble into ash. 
Mildly Neutral Aligned. 
Enhanced Magic: Spells and spell-like abilities that use negative energy are maximized (as if the Maximize Spell feat had been used on them, but the spells don't require higher-level slots). Spells and spell-like abilities that are already maximized are unaffected by this benefit. Class abilities that use negative energy, such as rebuking and controlling undead, gain a +10 bonus on the roll to determine Hit Dice affected. 
Impeded Magic: Spells and spell-like abilities that use positive energy, including cure spells, are impeded. These spells and spell-like abilities can still be used, but a successful Spellcraft check (DC 15 + level of the spell) must be made to do so. Characters suffer a -10 penalty on Fortitude saving throws made to regain negative levels bestowed through energy drain while on this plane, though they may leave the Negative Energy Plane and make their Fortitude saves somewhere else.