Mundane versus magical beasts

Fantasy often makes a distinction between mundane and magical or supernatural beasts, which is often arbitrary and illogical. This distinction doesn't exist in 13th Age, which relegates all such things to Beasts. However, this sort of thinking still permeates the fluff to a much lesser degree. For example, the druid's beast form power states "Stick to four-legged natural predators, not creatures with supernatural abilities or the ability to fly." One of the listed aspects is the owlbear, which in other fantasy (outside Avatar: The Last Airbender) is considered a magical or supernatural creature. (The form itself is cosmetic, so even if this was ignored the druid still couldn't fly as a bird or petrify with a gaze as a basilisk.) How could this be explained from an in-character point of view without sounding silly?

Distinguishing elementals, spirits and undead

13 True Ways and Eidolons introduced the new types Elemental and Spirit. Sometimes the distinction between these and other types may be ambiguous. I will try my best to sort that out here. Later I should write a primer on spirits and related things.

Spirits are the souls and personifications of natural forces, abstract concepts and emotions. They may overlap with spectral undead, in which case the GM could decide that spectral undead automatically qualify as both undead/spirit types.

Elementals are seething masses of base matter animated by demons, spirits, undead or similar entities. Constructs and elementals are similar because their bodies are composed of base matter and both have animating spirits bound into them. Some sourcebooks have included spontaneously animating constructs. The distinction is that the two are tied to opposing magical winds: constructs to artifice, elementals to nature.

Constructs and undead are pretty similar, being animated masses of something which isn't alive but might have been in the past. The difference between them is that they are tied to difference magical winds: constructs are tied to artifice, undead to death.

Not everything made of something other than flesh is an elemental, however. It is entirely possible for beasts and humanoids to have alien physiology based on fire or crystals or whatever. The reason why they aren't constructs or elementals is because they have a living metabolism: they eat and reproduce just like other living creatures.

The Winds of Magic

As modern humans we take it for granted that the fantasy world operates according to real world physics with magic added to let us cheat. Unifying magic and nature requires detailed explanations about how physics in the fantasy world is fundamentally different from our own reality.

The Crusader and the Priestess: strange bedfellows?

The Crusader and the Priestess, as well as their patron gods, are ultimately on the same side: the side of Ma'at. They serve order, balance, and justice, though in dramatically different ways. The Crusader, viewed in the most positive light, is a morally ambiguous man who makes difficult moral decisions.

But Order and Balance are not necessarily the same thing. If left unchecked by Balance and unopposed by Chaos, Order would ultimately petrify the universe like a fly in amber.

Since the current age is one where Chaos is ascendant, then Order and Balance work together to oppose it. But in another age this could quite easily turn around, and the heroes would be recast as freedom fighters against an oppressive regime.

Aberrations and Abominations

Aberrations have always been poorly defined. Sometimes they're just weird, sometimes they're affiliated with Cthulhu. Guides to designing monsters, like A Magical Society: Beast Builder, outright state the distinction is an arbitrary "I'll know it when I see it" sort of thing. That's not a stable foundation for world building, so I'm going to go ahead and give "aberration" a clear definition.

Demons versus Devils primer

Sometimes the distinction between demons (see 13th Age Core Rulebook) and devils (see 13 True Ways) may be a little arbitrary. I’ve devised this primer to provide guidelines for how to distinguish them clearly.

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)