Mystara Cosmology
by RipvanwormerThe Prime Plane is where Mystara is. It has stars, galaxies, planets, and so on. In the center of the galaxy is the biggest concentration of pure starfire in the known multiverse (rather than a supermassive black hole as in the center of our own galaxy), in which new stars are born. Alternatively, the Spelljammer cosmology could be used.
In another part of the galaxy is the Star Kingdoms, which is the ruins of the old world of Alphatia. In still another part was once the Galactic Federation in the time of Blackmoor, though this may no longer be extant.
There are parallel worlds accessible through planar travel, including LaTerre (a version of our own Earth inspired by stories by Clark Ashton Smith; the ancestors of many of the inhabitants of the Principalities of Glantri came from there), Aelos (a standard D&D world whose present existence was imperiled by a race of technological time travellers), and Eloysia (a parallel universe in which solar systems are bubbles of air in an infinity of solid matter, instead of being bubbles of solid matter in a vacuum). Other Ad&d worlds like Oerth and Toril are also somehow connected to Mystara's multiverse.
The Demiplane of Dread, home of the Ravenloft setting, has connections to Mystara. It may be the place where Castle Amber drifted for a time before it was returned to Glantri.
Limbo is a purgatory through which Mystaran souls pass on their way to the true afterlife in the Outer Planes. It's similar to 4th edition's Shadowfell, or to the Plane of Shadow. It's haunted by many undead.
The Dimension of Nightmares is an alien reflection of Mystara's multiverse, occasionally glimpsed in fevered dreams and night terrors. Its inhabitants are toxic to the life of the Prime Plane. It's been compared to the Far Realm. In 3rd edition, it was actually defined as a demiplane halfway between the Far Realm and the Plane of Dreams. Illusionists draw their power from this plane.
The Vortex Dimension is a place outside the known multiverse, beyond which even the Immortals cannot travel. Void hounds and umbral blots come from this plane on missions for the mysterious Old Ones.
There's also a faerie plane accessible in certain places of sylvan power. There's very little information on it apart from Tall Tales of the Wee Folk.
There's also a Spirit World, a complex plane of animal spirits, nature spirits, and corrupted evil spirits brought into close proximity with Mystara by the Great Rain of Fire (and described in The Golden Khan of Ethengar).
Touching the Prime Plane, the Astral Plane, and the Elemental Planes is the Ethereal Plane, which is pretty much the same as the standard Ethereal Plane you'll find in the Pathfinder game and the SRD.
The Elemental Planes, suspended in the Ethereal Plane and tied to the Prime Plane by wormholes, are Earth, Water, Fire, and Air. The standard SRD or Pathfinder versions of these planes could easily be used, but clasically they're presented as parallel reflections of the Prime Plane, with oceans of liquid element where Mystara has oceans, atmospheres of gaseous element, and continents of solid elemental matter where Mystara has land. Instead of humanoids, there are elementals, who have a sophisticated culture including art forms for all five senses. The Elemental Plane of Earth has oceans of lava and an atmosphere of choking dust. The Elemental Plane of Fire has oceans of liquid flame, continents of solid flame, and an atmosphere that's completely on fire. The Elemental Plane of Air has continents of solid air, oceans of liquid air, and an atmosphere of standard air. The Elemental Plane of Water has oceans of water, continents of ice, and an atmosphere made up of steam. Other planets on the elemental planes correspond with other stars and planets in Mystara's universe: moons made of water, stars made of earth, and so on.
A silvery membrane connects the Ethereal Plane with the Astral Plane. The Astral Plane is a bizarre place where mortals appear two-dimensional and everything is covered with a strange sparkling aura. The Astral Plane touches the Ethereal Plane and the infinite Outer Planes.
The Outer Planes are the homes of the Immortals of the five Spheres of Power, their servants, and the souls under their care. Known outer planes include:
Draesten, a shining, scintillating, chaotic plane of riotous life and energy of all kinds.
Brynn, a solid, flat plane full of rigid geometry. Nothing ages, grows, or decays on this plane.
Entrem, a plane made up of vast rivers of water that flow through space. This plane has strange temporal effects, so that visitors may exit in the past or the future.
Mirage is a misty plane of illusions, in which thoughts become real.
Pyts is a horrific plane of death, entropy, torment, and fiendish races.
Thorne is an Outer Plane made entirely up of giant thorns, seeming like an unending forest, part of a thorn bush the size of a planet. This is the home world of the phanatons and the planar spiders who are the ancestors of the araneas. This is the home plane of the Night Spider, an Immortal also known as Arachne Prime.
Chasm is a world of steep cliffs accessible from Thorne.
The Isle of Night is a plane under the control of the Immortal Nyx, accessible from the Dark Tower in Chasm.
There is also an outer plane of imprisonment in which the evil Immortal Arik is bound. The ancient reptilian carnifex are banished to another imprisonment plane (accessible at the end of a chain of seven planes corresponding mystically to the celestial bodies of Mystara's solar system), or conceivably the same one.
The Rainbow Bridge is a shining rainbow plane in which magic doesn't work. It leads to the Nine Worlds of the Immortal Realms, where the Northern Reaches pantheon dwells.
1. Asgard (home of the Immortals Odin, Thor, and Loki)
2. Vanaheim (home of the Immortals Frey and Freyja)
3. Muspelheim (home of fire giants)
4. Niflheim (home of frost giants and the Immortal Hel)
5. Alfheim (home of elves)
6. Svartalfheim (home of dark elves)
7. Jotunheim (home of giants)
8. Swergheim (home of dwarves)
9. Midgard, a parallel world similar to Earth during the Viking age. Some have speculated that this is the same as LaTerre, above, but during an earlier era.
10. Yggdrasil, the World Ash, which connects the nine planes.