Source Some additional information from PRG:OA
To an 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 Inner Planes, the most uncaring and intolerant of life. Only creatures immune to its life-draining energies can survive there.
The orthodox view of the Inner Sphere casts the Negative Energy Plane as the jealous rival of its positive-energy twin, an empty infinite void of entropic darkness antithetical to creation, fit only to consume and destroy.
Negative energy is itself a dark opposite of life-giving positive energy, yet while it is most often a source or tool of destruction, it is also the animating force of the undead. The ancient wisdom of occultism seizes on this seemingly paradoxical association with creation and posits that entropy clears the slate for what’s next as the multiverse inexorably marches along an unimaginably vast evolutionary cycle of its own. Perfection is not a fixed state. It is always growing and changing. To say that there is one “natural” state—for instance, utter oblivion—that constitutes perfection is as impossible as imposing a limit on the infinite. Occultists believe that this destruction allows for and drives change.
Nonetheless, negative energy sustains the undead, who throng to the sterile and desolate gulfs of nothingness that compose the overwhelming expanse of this dark and terrifying realm. The plane offers few solid surfaces, so the undead present here tend to be incorporeal and capable of taking flight on the soul-chilling currents that seem inexorably to guide visitors toward the absolute darkness at the plane’s heart. This inner blackness connects via portals to the black holes scattered about the cosmos of the Material Plane. Records of astral voyages to the Material Plane side of these portals relate tales of the accretion disks of black holes swarming with incorporeal undead trapped within the event horizon.
Within the plane, where the concentration of negative energy reaches an absolute, it begins to manifest a crystalline material that grows into beautiful and deadly structures of absolute entropy. When these crystals form strange angles, the plane gives birth to a sceaduinar.
These vile creatures hate life and unlife alike, and exist only to sow entropy and destruction. Somehow, their manifestation seems to drain a measure of the plane’s entropic energies, ironically making the regions around these haunting snowf lake structures the most stable and survivable regions in the otherwise hostile plane.
While negative energy is less of a concern, the sceaduinar themselves represent a significant threat to visitors.
The ancient wisdom suggests that the jyoti hate the sceaduinar for their knowledge of the role destruction plays in the creation of souls, and the jyoti fear the exposure of that information. The Negative Energy Plane’s most terrible and hateful residents, the undead abominations known as nightshades, care little for this squabbling between the planes. Theirs is a quest to eradicate all life in the cosmos, to cloak the stars of the Material Plane in darkness, and to quench the Cosmic Fire, no matter the consequences.
The Negative Energy Plane has the following planar traits:
Subjective Directional Gravity
Major Negative-Dominant: Some areas within the plane have only the minor negative-dominant trait, and these islands tend to be inhabited.
Enhanced Magic: Spells and spell-like abilities that use negative energy are enhanced. Class abilities that use negative energy, such as channel negative energy, gain a +4 bonus to the save DC to resist the ability.
Impeded Magic: Spells and spell-like abilities that use positive energy (including cure spells) are impeded. Characters on this plane take a –10 penalty on saving throws made to remove negative levels bestowed by an energy drain attack.