The Mortal Coil, or prime material plane, is the realm of mortals. The dominant thinking is that the Mortal Coil is three layers, combining spiritual essence with physical matter: Terra (also called the Mortal Realms or Fleeting Realms), in which all mortal worlds coexist; Annwn (also called the Faerie Coil or the Otherworld); and Ladinion (also called Deep Faerie or the True Otherworld). It is composed of a balance of essence from the Elemental Realities and Realms Beyond, and it is here that the various powers from the Realities Beyond play their game of cosmic chess. Both the Land of Dreams and Sea of Thought coexist with the Mortal Coil, and most of the first layer also coexists with the Demiplane of Shadow. The Mortal Coil's origins are unknown, but it is at least as old as the Realities Beyond. There are many theories regarding the origins of this plane.
One theory suggests that it was originally created by The Demiurge, a foul demonic creature. In the Time Before Time, the Demiurge, in its bid to overthrow the powers of Order and Weal, created a realm that mirrored its own hateful being. However, the Demiurge was cast down by a coalition of cosmic powers and much of what it made followed it into a hole in Creation and became The Abyss. Greatly weakened, the Demiurge became known as Demogorgon, the Devourer of Souls and Prince of Demons. The Mortal Coil is what is left of The Demiurge’s original creation.
Another legend popular to those that exist in the Beyond suggests that the Mortal Coil was engineered by the Circle of Three. Again, during the Time Before Time, the Circle determined that there needed to be neutral location where all powers could meet on fairly equal footing. Thus, they balanced the Mortal Coil with all aspects of Creation, incorporating bits and pieces of the Cosmos therein. Alas, the Circle of Three never finalized the process for they were pulled apart due to their disagreement regarding the Center. While the three parts of the Circle became The Supreme Virtue of Heaven, The Progenitor of Nirvana, and The Overlord of Hell, the Mortal Coil was left unfinished and unsullied by the will of cosmic beings.
However, the Cilidian offers another explanation. The Cilidian claims that what is currently the Mortal Coil is the remnant of a lost existence, a former reality that was partially resurrected. The guiding hand that accomplished this feat also guided The Others, incredibly powerful beings that are as far beyond the gods as the gods are beyond the lowliest of mortals. These Others reorganized the Mortal Coil in order to conceal and hide truths of the former Cosmos. To the Cilidian, the Mortal Coil (and arguably all of Creation) is nothing more than a great, shattered puzzle that masks a great secret. The Mortal Coil is a place filled with contradicting and striving forces that ensure that the major players are too busy to spend time uncovering the truth.
Whatever the origins of the Mortal Coil, once the opportunity arose, Chaos and Order were forced to co-exist and Good and Evil hung in the balance. Across the Mortal Coil, creation occurred. Stars and planets began appearing. Some of these were created by overpowers and/or divine pantheons. Others spontaneously coalesced from the disorganized elements omnipresent in the fledgling plane (though there may have been some hidden agency behind the development of these worlds as well).
A few planar scholars suggest that like The Abyss, the Mortal Coil possesses an infinity of layers. Such layers, they posit, may have vastly different laws than the known Mortal Coil. Flattened disks and worlds that are infinitely large are only two examples of the sorts of fantastic pictures such scholars imagine to exist in other layers. That these layers have remained hidden since the beginning, offering no evidence of their existence, bothers such scholars not at all. Other scholars scoff at this notion and insist that such inconceivable worlds on the backs of beasts or worlds that go in perpetuity can be found in a Mortal Coil comprised of only three layers.
