Ethereal Plane
The Ethereal is layered over all of material reality, arguably including sealed-off Realms such as Baatorand Carceri. From within the Ethereal, objects and creatures on the material appear foggy and out-of-focus. The material laws of physics become distant memories, and creatures float about by force of will.
Localized Phenomena
Creatures and objects in the Ethereal are invisible and intangible to the material. Conversely, the material realms are visible from the ethereal, but are intangible. Ethereal travelers report that moving through solid objects or creatures slows their progress, as if wading through mud.
Visibility is likewise difficult. Objects and creatures appear distorted, their colors blending and blurring nonsensically like a wet painting with a bucket of water dumped over it. The edges of objects likewise appear fuzzy and warped, their precise positions difficult to discern.
Climate
The Ethereal is under a persistent, swirling fog. Visibility is generally limited to 30 feet or less in all directions. The mists persist in a still climate, with very little wind in general, except for the Ether Cyclones.
Serpentine columns twisting through the fog, scattering it but never dispersing it, Ether Cyclones are extremely dangerous. Their exact nature is not well understood, but they seem to represent disruptions in the interface between the Ethereal and the Material. Creatures and objects caught in an Ether Cyclone can find themselves flung anywhere on the realms, including the airless sea of stars above it.
These cyclones appear abruptly and with very little warning, and affect spectral creatures and objects to the same degree as material ones.
Fauna & Flora
This plane is inhabited by spectral creatures, primarily ghosts, but most incorporeal undead can pass into and out of the Ethereal as well. A few other creatures have adapted to take advantage of the Ethereal; phase spiders, blink dogs, dimension beasts, and even an entire species of Dragon.