On Spirits

So here goes my primer on spirits and their consequences for the game world and rules.

Spirits are anthropomorphic personifications of abstract and physical concepts.
They lack body-soul duality. If you try to steal their soul or they try to possess someone else, no soulless body is left behind. If a spirit is damaged to the point of death it is usually banished rather than destroyed and may reform in the future. Spirits are generally sexless (but may express a gender) and unable to reproduce (but some have offspring with mortals), with special exceptions.

Sources: Encyclopaedia Divine: Shamans, Relics & Rituals: Excalibur, Mythos: The Animae

Three primary distinctions

Primordial spirits: The primordials were the first spirits to come into existence from the primordial chaos, predating the distinction between spiritual and physical. They personify abstract fundamental forces: the Archons of Order, the Achamoth of Chaos, and the Aeons of Balance. (These names are taken from Gnosticism, and unlike other monsters they loosely emulate their namesake.) [Aberrations, Abominations, Asuras?]

Terrestrial spirits: Everything in the material planes, even the planes themselves, has physical and a spiritual aspect or soul. Humans and their ilk have animi; animals, forests, rivers, mountains, and light have terrestrials. The latter exist outside of but still tethered to their physical counterparts. Most of the time terrestrials slumber in the near ethereal unless their physical counterpart is disturbed.

Ephemeral spirits: The thoughts and emotions of living things leave residue in their surroundings. As this ambient emotional energy collects it produces ephemera (sing. ephemeron). Ephemera are so named because they lack physical counterparts to anchor them and must consume the emotions that spawned them.

Other spiritual states

Subcategories of spirits include aberrations, celestials, elementals, fey, fiends and manifestations.

• Aberrations are spirits that originate from primordial chaos, outer space, nightmare worlds and aborted planes. They include aeni qael, akata, denizens of Leng, mâlites, proteans and qlippothim. [Origins in other planes of existence (primordial chaos?), outer space, nightmare worlds (dreams of mad gods?), aborted planes (a possible future, the previous universe, an alternate timeline?), and mad wizard experiment? (That's silly!)]
• Celestials are spirits born of of law and light or created by the gods thereof to oversee the workings of the world. They include angels, couatls, kami, lammasu, pegasi, psychopomps, shedu, sphinxes, and unicorns.
• Elementals are spirits born of the elemental chaos, representative of one or more elements. An elemental is a dual entity consisting of a soul inhabiting a body of base matter. The animating soul could be of any kind: spirit, demon, undead, etc.They include atronachs, gargoyles, genies, jyoti, mephits, sceaduinar, verms, and weirds.
• Fey are "souls that have been given one last chance at existence" (see The Complete Guide to Fey p8). Rather than a class of related spirits, to be fey is a state of being not unlike—albeit inverse to—undeath. They include azatas, blink dogs, dullahans, hags, nuckelavees, nymphs, and satyrs.
• Fiends are spirits born of evil. They include the endless varieties of demons and devils.
• Manifestations (see Relics & Rituals: Excalibur) are spirits born of strong desires and emotions. They include animate dreams and the spectral dead.
• Unborn (see Book of Hallowed Might)