The Plane of Negative Energy is the plane of Entropy, the source of substance and form in the universe. It has been paradoxically described as a semi-solid inky black void with no discernible orientation. Only undead or creatures such as an avatar of Death can survive on this plane. Even with the aid of magic or divine intervention, death is minutes away for travelers. In more ways than one, this plane represents the end of time. Like the Positive Energy Plane, it existed before the Multiverse and simultaneously existed after.
As the plane of substance (considered to be a plane of pure Yin and truly primordial), chunks of material can be removed from the plane under the right circumstances. Ancient advanced civilizations on the Prime Material Plane developed technologies utilizing matter magically secured from this plane to obliterate their enemies in battle.
Natural Resources
In the Border Ethereal that overlaps with the Plane of Negative Energy, there is a mysterious ethereal version of concentrated negative energy and matter.