Humans

Humans are humans. Not sure what you expect. They're the most common species here.
They can't inherently possess magic, but make use of studied spells known as "arcana" to get by this (more on that within the Magic Notes). They can sometimes have anomalous properties, like those with non-human relatives, but this is rare.
Most humans won't ever meet a supernatural entity in their lifetime, or at least knowingly, as there simply aren't very many of them compared to humans. Of course, there are exceptions, like those that live in "Bastions", areas with a high supernatural population. (This, unfortunately, has led to a very small group of people who believe supernatural beings don't exist at all.)

Fairies

Fairies come in all sorts of forms, varying way more than most species, but most look relatively human, with some odd features and distinct "wing-shaped" ears.
Fairies, while not immortal, do live considerably longer than humans.
They're born from (or if not originally a fairy, bound to) a landmark or area; being near this raises their power considerably, sometimes giving them the ability to change reality itself.
- A fairy's domain has no impact on how strong they are, per se– just because someone is bound to a very small space doesn't mean they're guaranteed to be weak.
- While this is rare, domains can overlap with each other.
Humans can become fairies via isolation and exposure to a lot of magic over a long period of time; the kind of magic can potentially affect what they're eventually bound to.
Various fae spaces are scattered around the world, seemingly existing in a dimension separate to typical reality.
- There were fae courts established in these realms, but their power over those belonging to them has waned in recent years, and are now kept going for the sake of tradition.
Fairy magic tends to focus on rules and etiquette, and the loopholes needed to get by them. Natural and some types of metaphysical fairy magic in particular is bound by 'the laws of nature' and 'the laws of physics'.

Subspecies

Each subspecies is differentiated by the location/landmark they're bound to. This affects their abilities and appearance. There can be overlap to these categories, and there's much more than the ones listed here.

Fairies of the Tide: Fairies bound to bodies of water, and areas near bodies of water like coastal cliffs and beaches.
Fairies of the Stone: Fairies bound to rocky and sandy areas, like caves and deserts.
Fairies of the Hearth: Fairies bound to man-made areas, usually older areas like ruins and sections of big cities.
Fairies of the Living: Fairies bound to inland areas with large amounts of flora, like forests and plains.

Angels and Demons

While angels and demons are distinct, they are essentially interchangeable. They usually have a true form and a more humanoid form; an angel's true form is quite painful to look at.
- The same can be said for angel eyes, which are typically covered. That being said, angels have several eye tattoos on their body that move and function as actual eyes. These tattoos disappear upon falling.
Note that "demon" is a colloquial term for fallen angels, and might mean something else outside of places with a notable angel population (e.g. Mahou Reps sometimes being referred to as demons).
Angels become demons due to very, very extreme stress or hopelessness, and all the emotions that can cause those. It's theorized that demons can revert back to angels, but the method to do so has yet to be found.
Angels can be born from the light found in Heaven, and it remains in them unless they fall, where it's all released. From then on, if they attempt to enter Heaven, ambient heavenly light will attempt to enter them again and basically overload their body, causing them to start burning.
All are able to summon a weapon, usually some kind of blade (with rare exceptions, like Morningstar's shotgun). Said weapon can be made more powerful using souls; this doesn't "use up" and destroy the souls. Usually.
- They also possess pyrokinesis and minor shapeshifting abilities (some are more adept shapeshifters, however).
There was meant to be a massive war between angels and demons centuries ago, but eventually most lost interest, and some even forgot entirely.
As they're name-dropped in various spells, blessings, and other shenanigans, angels and demons are usually referred to by their chosen "last name" (or just a nickname) in casual conversation, and calling them by their first can be considered overly personal or rude. This is a little dated now, but it still remains as a cultural thing.
Humans can potentially become angels or demons after death, usually by dying while in Heaven or Hell.
"Half-fallen" refers to angel/demon-hybrids, which typically occurs by being born that way. They can't change to either angel or demon– they're stuck like that.

Subspecies

Both angels and demons are ranked in power by the typical nine angel hierarchies, and tend to be placed in specific positions within Heaven's offices (but it's not a hard-and-fast rule). The following info is for angels still in Heaven, so job descriptions are less relevant when referring to Earth-bound angels, or demons. It's possible to move up ranks, but this is very hard and unpredictable, and it only gets more difficult the more powerful you get.

Seraphim: Extremely powerful, with very specific and important jobs. These are the only ones who possess halos and wings while in humanoid form, and are very few in number.
Cherubim: Relay information to Seraphim from the other ranks, and are the only ones besides Clark allowed in the archives; also function as security to some degree. Sometimes have multiple limbs and/or heads.
Thrones: The security within Heaven, who will occasionally try to de-escalate things on Earth. Their magic has a unique, ring-like appearance.
Dominions: The angels' upper management. Usually stays within Heaven at all times.
Virtues: Miracleworkers, and are involved with some older forms of arcana. Usually possess elemental or metaphysical abilities.
Powers: Assist in sealing off dangerous forces, often within themselves. They have an immense amount of self-restraint.
Principalities: Are enlisted to protect large groups of people, and relay messages to Earth. Usually, they have stuff on their heads, like horns or antennae.
Archangels: Are enlisted to protect smaller groups of people, or individuals. Usually have a deep understanding of fighting tactics, as it kinda comes with the job. Some archangels do not have a form besides their human one.
"Classic" Angels: Unremarkable angels. Most angels or demons who were previously human are a part of this rank. Usually they're hired as guardian angels, along with archangels. Most from this rank do not have a form besides their human one.

Vampires

Vampires are exactly what you'd imagine.
They can survive without drinking blood or eating anything raw for quite a long while, potentially for years; however, they can't (and should not) avoid it forever.
Vampires can't turn other vampires, unless said vampire was afflicted with a specific curse targeted towards nobles that originates back in the 1700s. Said vampires are understood to mostly be rich dickheads and to be avoided.
Some vampires, however, were turned through other means, like botched resurrections or transformation spells.
Most of the "weaknesses" are just myths or a side-effect of that aforementioned curse, but vampire eyes tend to be pretty photosensitive, so there's some truth to the "can't be in daylight" thing.

Ghosts (and Souls?)

Souls are generally understood to be powerful manifestations of the self, but that's about it. A decent amount is known about the nature of souls, but it's very little compared to what isn't known. As the self is not unchanging, souls are decently "malleable" and can be altered in various ways, although direct manipulation is very challenging.
Not all species form souls, nor do all species have similarly functioning souls (e.g. fae souls being highly unstable and usually unable to persist after death).
Souls are more or less the arcane equivalent of a Swiss army knife, and have numerous uses in several kinds of arcana. (This shouldn't damage or destroy it. Shouldn't.) However, heavy reliance on souls is regarded as amateurish at best and genuinely horrifying at worst.
- If this is sounding familiar, you can probably guess that angels and demons' aforementioned ability to use souls with their weapons runs on this same concept. Soul usage is a bit more frequent with this demographic due to naturally being able to take advantage of it like this, and practically runs rampant in Hell, which has unfortunately seen the rise of especially disconcerting applications of this. (Heaven Corps has put very strict guidelines in place concerning the use of souls in arcana.)
Souls are autonomous to a degree but seem to run on their subconscious alone, slipping in and out of other planes almost completely at random when not affected by external forces.
Ghosts are souls that through one way or another– typically via high residual emotion and sheer willpower– begin to display at least some sentience, and often can create various paranormal phenomena.
They can still move through planes, but it's one of those things you just do unthinkingly, so it's difficult to do on command.
Ghosts can appear as a full apparition, or as a will o' wisp indistinguishable from a standard soul to the naked eye. Showing up as an apparition takes more effort, so it's easy to tell if a ghost is stronger than normal if they can hold this form for a long time, or indefinitely.
All ghosts can possess objects and entities. A ghosts' mental state will begin to deteriorate if left without something to inhabit for an extended period of time (this period varies from case to case), reducing them to base desires such as fulfilling "unfinished business". Possession can help keep them grounded and heal from this (which also varies between individuals), so ghosts are often found alongside a frequently-haunted object or two– or even with an entire location under their control!

Mahous

Mahous are technically not a species, per say, but they're here just to be thorough. Further detail can be found in the Mahou Subset Guide.
They're similar in nature to familiars, even if the underlying magic behind it is a little different. This means any, and I mean any entity can become a Mahou through the necessary ritual. (However, this section will be focused on human Mahous, as information on non-human ones are basically nonexistent.)
- A Mahou's patron, known as a "Rep" in the community, can also potentially be anyone and anything. However, it's much more taxing, so Reps tend to be extremely powerful. Each type of Mahou under a certain Rep is known as a "subset".
They have in-uniform and normal forms; basically, just picture how magical girls work. Thankfully, the transformation process is way faster than a magical girl transformation. The uniform can be altered to some degree.
- For whatever reason, the magic associated with Mahous is particularly reactive to most camera technology. Mahous tend to have some kind of odd alternate appearance when filmed or photographed. In a similar vein, magical records and such are heavily obfuscated by Mahou magic.
Mahous are bound to their Rep by a core embedded in their body as well as a part of their uniform known as the "tie", usually worn around the neck.
- The core is the source of power granted from the Rep, and of course differ in characteristics depending on said Rep. Most Mahous need their core to function and/or live– this is very apparent in the case of human and human-adjacent Mahous, where the core literally replaces their heart. (Please do not ask Mahous if you can try to feel for a heartbeat. It's rude.) Mahou cores dissolve upon death, and breaking a core while the Mahou is still alive can cause a small explosion at best; the specifics depend on the individual. However, with the right power, you can safely recover a core...
- The tie is what keeps the Mahou and Rep in a psychic bond, meant to regulate the core and allow for easy use of the provided abilities. However, that mental link works a little too well; the Mahou's personality tends to be influenced by the Rep (usually unintentionally, but some Reps have taken advantage of this). If the Rep is ill-equipped for their current situation, this can even go both ways. Despite clearly being an accessory, the tie feels like a part of the Mahou's body.

Subspecies

Aside from subsets, there are different categories of Mahou, which are usually differentiated by how they're connected to their Rep.

Improper Mahous: Mahous who incorrectly did their ritual and survived, and thus have a strained connection to their Rep. They tend to have powers that stray from the norm for their subset; they're weaker on average, but Improper Mahous can potentially have very strong abilities due to a mostly unregulated core. However, this may come with health issues.
Former Mahous: Mahous who remove their tie (which is very painful, by the way!) and cut off their connection to their rep. This causes their core to become unstable, and irreversibly corrupt the Mahou– letting their powers go haywire and slowly transform them into whatever their Rep is, or something similar. Former Mahous are stuck in-uniform for some time after they remove their tie.
Awoken Mahous: Mahous who build up an intense amount of power and become incredibly in-sync with their Rep, transforming them into an alternate form with all the same abilities as their Rep. Both parties can communicate directly with each other through the psychic link in this state. However, achieving an Awoken Form can be harmful to the Mahou, and possibly the Rep as well.
- Permawoke Mahous: Mahous who, for whatever reason, are naturally on the same wavelength as their Rep, and are on the verge of becoming an Awoken Mahou by default. This is very rare. Becoming aware of the Rep's influence, and being able to tell between that and your own thoughts is also a good way to achieve this (paradoxically enough).

Messengers

Messengers are powerful and mildly omniscient aliens, with qualities strangely similar to that of Earth's plantlife. Their true form is fine to look at initially, but long exposure can lead to nausea and might even cause some to pass out.
Note that "messenger" is a completely non-diegetic term; there is no proper name for this species, because until now there's only been like... one of them.
They have immense shapeshifting capabilities; however, noticeably changing their size takes much more energy to hold and thus weakens their power quite a bit.
Messengers possess power over sleep and the Dream World, each getting their own personal space in said dream world. They also can draw power from emotion, albeit the degree to which they can do so differs between individuals.
The thorns in their true form are retractable, and exist regardless of the type of flower they resemble.
Only two messengers are currently known to exist: Nyarlat, the first messenger in existence, and their Former Mahou, Carmen Carter.

Dark Young

Dark Young are children of what is presumed to be the Rep of the Echo subset. They loosely resemble wide, dead birch trees with many goat legs for roots and several eyes around the "trunk". Despite their appearance, their body is more akin to rock.
They are sometimes summoned as familiars or bodyguards in areas more exposed to extraterrestrial contact.
Other entities can conduct a ritual to be reborn as a dark young hybrid, sometimes erroneously referred to as "satyrs". (Note that this is different from an Echo Mahou removing their tie.)