Mystara cosmology and 3E Material of the Planes - Material Plane
by David KnottThe 3E Manual of the Planes actually greatly simplifies the task of describing the planes in a cosmology. After reading through that book, I took the plane and dimension descriptions in Wrath of the Immortals and ran them through the newest 3E book and found that the information in WotI is clearly consistent but incomplete in terms of the 3E MotP.
Terminology: There are two terms from WotI for which the 3E MotP uses different words: "Dimension" becomes "cosmology" and "node" becomes "Portal created by Immortal".
Traits of Material Plane: In most respects, the Mystaran Material Plane matches that given in the 3E MotP, with the following exceptions:
Pantheon: The most noticeable difference is that Mystarans revere a pantheon of Immortals who generally have little in common with the deities of other settings.
Gravity: Gravity is normal on the outer surface of Mystara. Elsewhere on that plane, gravity may be of any type except subjective directional.
Connections to other planes: In the standard "Great Wheel" cosmology, the Material Plane is connected to other planes via the Astral Plane, the Ethereal Plane, and the Plane of Shadows. The 3E MotP describes in detail the consequences of eliminating any of these planes from a given cosmology.
Astral Plane: Here we have evidence of a strongly negative nature about the connection between the Astral Plane and the Material Plane. The Alphatians clearly reached the Material Plane by a route that can be simplified to the following: Old Alphatia to Draesten to Astral to Ethereal to Material. In the 2000 years since their arrival on Mystara, they failed to discover any more direct route through those planes. Given the basic nature of such spells as Astral Projection, I would take this failure as evidence of a lack of direct connection between the Material and Astral Planes.
However, when we look at the sidebar about the consequences of eliminating the Astral Plane, we see that most of the effects mentioned as not working without an Astral Plane do in fact occur on Mystara. Mystarans clearly can teleport and summon monsters from other planes, although the evidence for them casting Astral Projection is non-existent. In combination, the available information would indicate that the Mystaran Material Plane is indeed disconnected from the Astral Plane -- but some other plane (of which two likely alternative candidates are named in the 3E MotP) serves to provide the planar connections that the Astral Plane would normally provide.
Ethereal Plane: There is no question that the Mystaran Material Plane is coextensive with the Ethereal Plane and that the Ethereal Plane provides access to (at least) the Astral Plane and the four Elemental Planes. Since the Astral Plane is totally disconnected from the Material Plane, we thus have evidence that the Ethereal Plane extends beyond the Material Plane and thus that the Mystaran Ethereal Plane has a Deep Ethereal region.
Plane of Shadows: In the 3E MotP, this plane is intended mainly as a way to move between the Material Planes of alternate cosmologies. From available Mystara/OD&D material, the evidence for any sort of connection between the Mystaran Material Plane and the Plane of Shadows is rather weak, consisting of exactly two items: The Project Image spell and the Nightshade class of monsters. However, if we re-interpret the Project Image spell as being "Illusion (Figment)" rather than "Illusion (Shadow)" and don't require the Nightshades to have been able to reach Mystara directly from the Plane of Shadows, then the necessity of such a direct connection is eliminated, thereby making travel between Mystara and other settings more difficult.
For the two alternate cosmologies named in WotI (Myth and Nightmare), it is not at all clear that either one required access to the Plane of Shadows for contact. The Nightmare cosmology appears to have been reached via the Astral Plane or the Region of Dreams, while the Myth cosmology access the Mystara cosmology via portals that could not be rebuilt once they collapsed. In summary, it is not at all clear whether the Mystara Material Plane is connected to the Plane of Shadows -- but if it is, few if any Mystaran spellcasters have figured out how to exploit that connection.
Other planes: Of the variant planes listed in the appendix to the 3E MotP, there is evidence that the Mystara Material Plane is connected to the Region of Dreams (per Prince Jherek's Secret Craft in GKoM), the Plane of Mirrors (per the module "Skarda's Mirror), the Spirit World (per Gaz 12 and the description of "Limbo" in a VotPA article), the Temporal Energy Plane (per "Chronomancer" and various modules involving time travel), and the Plane of Faerie (per PC 1). Limbo and the Spirit World are the prime candidates for providing access to the Outer Planes that would normally be provided by the Astral Plane -- but at this point even the Ethengarian shamans (the only ones with direct experience of the Spirit World) have no idea of the larger significance of either plane.