In Shadowgate, most basic planar mechanics can be assumed to parallel 2e/3e source materials, as they’re integral to the functioning of our history & magic. There are a few key changes, however, which are specific to our setting and are detailed below. Primarily we follow the ‘Great Wheel’ model of planar cosmology. Central to the wheel is the prime material plane, wherein the realm of Shadowgate and the other nearby continents lie. Overlapping with this are the ethereal, shadow, and feywild, and bordering it lies the astral. From there, the inner and then outer planes are accessed by way of the astral plane.
-Ethereal plane: a plane of ghosts and horrors, and a means to travel within the material plane or step out of alignment with it. Spells such as blink & displacement move the caster only for an instant onto this plane.
-Shadow plane: much as its name suggests, it is a plane of shadows upon deeper shadows. Dark and terrifying things eke out their lives, and unlives, here. The plane of shadows exists as a colorless echo of the prime, and it is the origin of all negative energy which filters through various crossovers into the prime material plane.
-Feywild: another echo of the prime, with points of contact in those wild places that still hold most strongly to its breath of life. This is the ‘light’ to the Shadow plane’s ‘dark’, and the upwelling of all positive energy which filters through various crossovers into the prime material plane.
-Astral: this is the plane that lies between the prime and the various inner & outer planes. A relatively empty and timeless place, it allows for travel between the planes.
These are the four elemental planes – air, earth, fire and water – accessible from the prime via the astral plane. A few tangible cross-points exist on the material (eg/ the plane of fire has a permanently tethered astral crossing point in the ruins of old Antioch, placed by the maddened wizard Ignatius). Beyond this, powerful magic must be used to reach these planes.
Many outer planes exist, although scholars still debate to this day as to their exact number and nature. Such planes are the realms of Gods and demons, celestials and devils, and the many splendors and horrors that lie between. Certainly reason would suggest that planes such as these must exist to encompass all deities, alignments and natures in some form. Amongst these also lies the Fugue plane, where the souls of the dead are drawn through the astral plane to await Kelemvor’s judgement.
Demi-planes are usually only small, and are physically created by a deity or powerful group of spellweavers. Countless exist, mostly only as tiny pockets (eg/ rope trick, bags of holding). Scholars also argue that larger, artificially made demi-planes could exist, but if they do, their nature is well hidden.