Ethereal Plane

''"It is a plane out of phase... It is a place of ghosts and monsters. It is right next to you, and you don't even see it." -Unknown''

Overview
The Ethereal is a cold, translucent plane of existence layered over the Prime Material plane. Life, matter and energy do not exist there naturally, and creatures or objects that find themselves trapped in the Ethereal cannot interact with the Prime Material world. The Ethereal realm is haunted by the souls of those who are unwilling to pass into the afterlife, and in the far, unexplored depths of the plane, there are said to be things worse than phantoms.

Physics
Gravity does not exist in the Ethereal plane, and sentient creatures can thus move simply by thought. Matter in the Ethereal ignores matter in the Prime Material, phasing through it as if it weren't there. However, the denser the Material object, the more difficult it is for an Ethereal object to pass through. Stone, silver, lead and gold are examples of anti-phase materials. Ethereal creatures also suffer harmful radiant effects from contact with living Material organisms.

Ghosts
On rare occasions when an unwilling soul leaves the Prime Material plane, the spirit may, if it's will is strong enough, refuse to pass on. This creates the disturbing phenomena of ghosts, who find themselves lingering in familiar places, and phasing between the Ethereal and the Prime Material. These lost spirits are often confused, frustrated, and full of negative emotion. Most phantoms desire to complete unfinished business from their former lives, and such spirits may not even believe nor remember that they died at all.

Known methods by which to safely send ghosts into the afterlife are by either slaying the spirit with magical weapons, or satisfying their need to cling to the Prime Material.

Monsters
Though few have ever been seen or documented, phase spiders are known as the Ethereal's deadliest predator, possessing the capability to phase between the Material and Ethereal planes of existence at will. Little is known about them, and none have ever been captured for study. Reports describe them as having white skin with blotches of blue, and only two eyes instead of eight like most arachnids. Because of this anomaly, as well as their body shape, ethereal webs, and plane-shifting capabilities, it is surmised that phase spiders may come from the deep unknown of the Ethereal itself.

Trivia
Like some demiplanes and pocket-worlds, the Ethereal plane is full of breathable air.