Ah, spirits. Perhaps no other fantastic beings in all of fictiondom can be as vague as to what they are than them.
There are several questions you have to ask, though, if you wish to have them in your story:
Are they immaterial/incorporeal, and if so, to what degree?
- Some are immaterial, but they can take material form if they choose to.
- Some are often seen in a material or semi-material form, but still don't seem to completely follow the laws of physics one would expect them to.
- Others exist inside of or are bound to a physical vessel (such as a tree, lake or stone, a pile of garbage, etc.), which may be either treated as their home, or as their body, although in either case the spirit will usually be capable of manifesting or affecting the world beyond without making its vessel into an Animate Inanimate Object.
- Regardless of anything else, they can often turn invisible.
- Sometimes they can't, usually they can (which doesn't mean they will). Sometimes they will only possess a willing host, other times they're not so benevolent.
Where do they live/come from?
- As one might expect, spirits often come from the Spirit World, but any generic Magical Land will do in a pinch.
- The relationship between the Spirit World and the mundane can vary though, sometimes being a wholly separate place, sometimes being an overlay on the normal world.
- Sometimes they don't come from anywhere "other" at all, being a natural (if frequently invisible, or often remote) part of the world.
Are they mortal/ageless/invulnerable/killable?
- The majority of them are killable, usually through one of their specific weaknesses, occasionally via more mundane means. You may only be Fighting a Shadow, however.
- Almost all of them are Immortal, barring a few exceptions.
- Sometimes spirits are closely tied to the health of a particular region (a town say, or a forest). Damaging or destroying that region will often destroy or at least weaken them... unless it just pisses them off instead.
Are they capable of evolution/change?
- Varies heavily. Many have Voluntary Shape Shifting abilities, though not all. Some demonstrate a sort of reverse-Fisher Kingdom effect, mutating or changing in response to their environment. Some are timeless, and often stuck in a Medieval Stasis to boot. You can expect them to have some problems handling more modern advances (whatever that means for the setting), though there are always exceptions.
Can they be consumed/deformed by other beings?
- Spirits can be often be used by others (including other spirits) for power, perhaps unwillingly.
- A deformed spirit may end up as a Broken Angel. Or an Eldritch Abomination.
What powers do they have?
- Some type of magic is almost mandatory for all of them (most are Made of Magic in some way or another, after all). However, spirits can be any power level, from less potent than a human (despite their magic) all the way to, for all practical purposes, being gods. They tend to be on the mid-weight-to-moderately-high end of the spectrum, though.
What weaknesses do they have?
- They're often able to be sent back to wherever they came from (or barring that possibility, still sent running).
- Magical items (and magic in general) are usually able to hurt them (and sometimes are the only things that can). If spirits are treated as free-floating souls, expect magics capable of manipulating or damaging souls to be particularly devastating.
What is their relationship to the natural world?
- Sometimes spirits are associated with, a part of, or even representatives of the natural world. Sometimes they are wholly alien beings beyond the comprehension of normal reality. Sometimes they're both.
...And to humanity?
- Sometimes spirits and humans get along swimmingly. Sometimes they don't, for whatever reason. Sometimes, even if they only get along uneasily, humans will seek them out for power. Sometimes it varies by the variety of spirit (or even just the individual spirit in question).
What is their relation to...note
- The "good" (usually) spirits.
- The "bad" (usually) spirits.
- Fae spirits come in two flavors;
- The mischievous yet non-evil kind, such as pixies and sprites.
- ...and the "I left you a changeling that's making you soup with a special ingredient, otherwise known as your actual child" kind.
- Fae spirits come in two flavors;
- ... youkai?
- Spirits...from JAPAN!
- ...the undead, particularly ghosts?
- Ghosts and similar entities tend to be the souls of beings that haven't moved on, and thus become spirits.
- They tend to be the biggest, baddest spirits around, and they often control lesser spirits.
- ...embodiments of the elements and concepts?
- ...and any number of other mythological beings.
Are they good? Bad? Whatever?
- Their morality is mostly based on what type of spirit they are, and sometimes it varies from individual to individual.
- In Bleach, ordinary human spirits are called "Pluses," usually created when someone dies with Unfinished Business. Pluses tend to stick near places or people that were important to them in life (tethered to the location by a long chain), and sometimes might even realize that they're dead. However, since they're Invisible to Normals, they slowly grow resentful and insane through isolation and/or neglect. When this begins, they turn into spirits called "demi-Hollows", which are still normal Pluses with a hole slowly growing on the spot where their chain is connected, symbolizing their decaying connection to their humanity. When the chain has eroded all the way (or when external factors prompt a change), they become full Hollow with an unquenchable thirst for souls. If a shinigami sends the soul off to Soul Society (the afterlife), they'll be safe from transforming into a hollow, but will now begin a second life living in a poor, destitute city based roughly on feudal Japan. The lucky few qualify to become shinigami themselves (although, given the average life expectancy of a shinigami, how "lucky" this is can be disputed). The shinigami and Hollow also have their own hierarchy and ranking, and despite being the "good guys", the shinigami are essentially nobility and treat normal Pluses at best with indifference and at worst with contempt.
- Date A Live's Spirits are beings which are occasionally sucked into this world, causing "spacequakes" (a phenomenon that destroys everything within a spherical area of effect) in the process. And they happen to be top class Bishojo as well. To stop them from wreaking havoc on this world by accident, without killing them? The main character Shido has to date them. The real kicker? It's revealed later in the light novels that all Spirits used to be normal humans until they were transformed via the Sephira crystal.
- The Passengers of Revival are explicitly the souls of revivers. They are persistently visible to humans and cameras, can move like a gas, cannot cross salt, can be physically restrained, and can be killed by drowning.
- In Grim Grinning Ghosts when Harry is killed at seven he "splits" into a spirit and a zombie, with the ability for the former to possess the latter, giving an illusion of life.
- The high spirits of Adam R. Brown's Astral Dawn series are very different from the average spook found haunting houses. The high spirits were once mortal humans before they died and ascended to Averya (Heaven) or Nazyra (Hell). They evolved to become so powerful, they gained total dominion over their created worlds and even revisited Earth to become the gods and legends of ancient mythologies.
- The souls of the dead in The Divine Comedy are referred to as "shades" because while they may appear to have bodies, they cannot interact with physical people like Dante or project shadows. The shades only appear to have bodies that feel pain and pleasure so they can experience some of what eternal life will be like while not having to wait until the Last Judgement.
- In The Dresden Files, Humans are made of three things: Body, Spirit, and Soul. Ghosts and some creatures from the Nevernever are made of only Spirits and other creatures from the Nevernever (such as Fae) are made of both Body and Spirit. Finally, some very special kinds of ghosts can have both Spirit and Soul.
- Beings from the Nevernever can be summoned or cross over on their own. For those without bodies they can create material bodies for themselves made of ectoplasm, which dissipates without a trace if they are killed or leave (or no longer have enough magic to maintain the body).
- Certain kinds of spirits (ghosts, demons) can possess humans and animals (e.g. cats) but not all of them, apparently. Permanent bonds are possible via mutual pledges of loyalty.
- All spirits seem ageless, but they're not invulnerable.
- Spirits always stay the way they are.
- They can be consumed/deformed by other beings, usually by bigger and meaner spirits, though mortal wizards can feed on them, too.
- Since spirits are incapable of evolution, their True Names never change, and whoever knows it can force them to do their bidding.
- Henrik Wergeland developed an entire spirit lore, which surfaced in his own mythology pretty early. Essentially, he imagined a kind of "elementary spirits" roaming the heavens (like swans swimming on the "Milky way river"). Those spirits could "lay eggs" in the human souls. Now that is one way to explain it. Furthermore, one spirit could actually split in two, to harbor more than one soul (or more). In this way he explained his sense of companionship with his muse, Stella (actually a quite physical girl he was madly in love with). Only from time to time would a spirit enter a single soul without splitting up. The result would be a person with great historical impact, like, for instance, William Shakespeare...
- In Lord of the Rings and the rest of Tolkien's verse (The Silmarillion, The Hobbit, The Children of Húrin), there are basically two kinds of spirits. The first, Ainur (Valar and Maiar) are the local version of angels and demons (ie. Valar and Maiar begin as angels, but can become corrupted and turn into demons); they exist simulataneously in two worlds (wraith-world and the real world), can change shape and become immaterial at will (unless they are in Mode Lock like Gandalf and Sauron), are immortal and happy about it, come from Valinor and are the source of most Functional Magic in the verse. The second type (Nazgûl, Wraiths, ghosts etc) are spirits who were once souls of Men (or Elves), they live mostly in the wraith-world and have problems interacting with the real world, are usually immaterial, immortal but remarkably not happy about their condition and have less powerful magical abilities; they are also likely to be evil, because souls of good people obediently go to the halls of Mandos to reach the afterlife (though the Nazgûl, at least, are actually victims of The Corruption).
- Masquerades in Akata Witch, which are not to be confused with The Masquerade or Masquerade Ball. They are spirit creatures, and they will hurt you.
- The Stormlight Archive has the spren, which are associated with various phenomena. Whether they're drawn to said phenomena, created by them, or cause them is not clear to most people in universe. These phenomenon include wind, rain and fire, natural processes like rot, emotions like fear and passion, and even more esoteric things like music, creation, and honour. Some spren can move small objects and give small pinches of energy, as well as mimic voices.
- The nature of spren has been expanded upon gradually over the course of the series. They are essentially pieces of power given a kind of life by people's ideas about various phenomena. They exist naturally in the Cognitive Realm and are drawn partially into the Physical Realm by the phenomena they are associated with. Most spren are essentially the Cognitive Realm equivalent of animals, whereas others are intelligent enough to form societies. Some of the kinds of intelligent spren are able to form bonds with humans that grant the human magical powers, while allowing the spren to think while in the Physical Realm (without a bond they are nearly mindless outside the Cognitive Realm).
- Christopher Paolini's Inheritance Cycle has spirits as one of the many intelligent species in the setting. They are described as being hovering orbs of light constantly changing in size and color, but very little else is understood about them. One of the disciplines of magic involves summoning spirits and using them as mana batteries, which is never really shown in action but is presumably extremely powerful since spirits that we do see are capable of no-selling mental defenses and pulling off feats of magic that even dragons would consider impossible. The user of spirit magic has to be careful not to summon spirits more powerful than they can control, however, since spirits can take control of a human body and form a Shade. Even though one of spirits' few established likes or dislikes is the fact that they absolutely despise sharing a human body, they will always try to do this when summoned and can only leave a possessed human when the Shade is killed. Perhaps because of this, despite spirits' typical Blue and Orange Morality, Shades are universally Always Chaotic Evil.
- Spirits in The Reunion With Twelve Fascinating Goddesses are supernatural beings that live in the other world. They dwell in everything, including the air, earth, water and plants. Low level Spirits have the forms of animals, while Deities have human forms. Humans can make contracts with them to use their power.
- Religion... as in all of them. Trinitarian Christianity has the Holy Ghost, Buddhism has Hungry Ghosts (although they're more like ghouls than conventional spirits), various religions and mythologies have regular ghosts and fairies/Nature Spirits/Little People, and of course Shinto and Animism have everyone. And everything.
- Suffice it to say, just about everything in mythology that wasn't human or a corporeal undead was either a spirit or descended from one.
- The Book of Spirits is the New World of Darkness book dealing with rules for spirits. They're generally the domain of werewolves and mages with the spirit arcana, but they can be dealt with by vampires and mortals as well.
- More specifically, nWoD spirits are incorporeal beings associated with concepts, Anthropomorphic Personification but usually without the anthropomorphic part. They sustain themselves by hanging around places associated with their concept; river spirits with rivers, grief spirits with funeral parlors, spirits of mugging with back alleys, etc. They can also try to encourage or nurture the concept that feeds them, which is bad news when dealing with a spirit of murder or something similar.
- Both Worlds of Darkness also give spirits a hierarchical structure, organizing them into courts with various ranks, but with different twists. In nWoD, each spirit is technically an independent actor that shares a Choir with like types - for instance, each dove spirit gets along with other dove spirits and is a member of the Choir of Birds. In cWoD, each spirit is effectively a "representative" of a greater totem, which may itself fall in with the brood of a totem more powerful than itself - for instance, each dove spirit is actually an aspect/representative of Dove, who is herself allied with the brood of Unicorn, and so forth.
- In Magic: The Gathering, Spirits are a creature type, essentially representing all disembodied creatures — from ghosts to nature spirits to some pretty weird things — that are't claimed by another creature type already, such as Elementals, Demons, Angels and Gods. With some exceptions, they aren't generally associated with any one color of mana. Their exact nature and importance varies from plane to plane:
- In Kamigawa (which is based on Japanese Mythology), they are known as Kami, and warred against the mortal races. They are for all intents and purposes gods, and some are pretty unusual looking.
- In Ravnica, they're primarily ghosts, due to the plane being trapped in its own little bubble in The Multiverse and not allowing the spirits of the dead to escape, forcing them to manifest on the physical plane. They are heavily associated with the Orzhov Syndicate, which uses them as guards and enforcers and is ruled by a ghost council, the Obzedat. That said, some spirits are known to be part of other guilds.
- In the Gothic Horror-inspired Innistrad, geists — the spirits of the dead — form one of the set's five gameplay tribes (alongside humans, werewolves, vampires and corporeal undead) and are chiefly associated with White and Blue mana — Black, Red and Green geists also occur, but arent common. White geists are traditional ghosts returned to watch over their families or fulfill duties or obligations; Blue geists are poltergeists born from compulsive behaviors, cause mental afflictions in people they torment and are attracted to water, fog and storms; Black geists return as predatory haunts and are very dangerous; Red geists are obsessed with revenge and failures from their mortal lives and are the most aggressive spirits; and Green geists are especially attracted to nature, often becoming the spirits of landforms, copses and so on.
- In the Classical Mythology-inspired Theros, the eidolon separate from their bodies upon death. While the corpses become the memory-less, shade-like zombies known as nostron, the eidolon also forget their past lives and wander around aimlessly, often drawn to the magic of the nymphs. They are generally represented by enchantment creature cards.
- Pathfinder has beings like kami, oni and other native outsiders that are referred to as spirits, though what exactly that means varies from creature to creature. Oni, for example, are formless ethereal beings that take forms resembling humanoid races, while kami are guardian entities that bind themselves to a particular charge. There are also occult spirits, the remnants of souls and minds for those too weak to manifest as undead but strong enough to communicate with and assist the properly attuned.
- In the Dragon Age series, spirits and demons are the same thing. They inhabit the Dream Land called the Fade but can be summoned into the material world (or enter it on their own in certain locations). They seem to be ageless but can be killed, whether in the material world or in the Fade. Both demons and benevolent spirits can possess humans, though the former tend to turn them into Humanoid Abominations. Each demon is associated with one of five sins (corresponding to the negative emotion it feeds upon); benevolent spirits seem to be associated with virtues but because encounters with them are so rare, no established classification exists.
- It also implies that spirits become demons by the perceptions of people. Or by a mage using blood magic to bind them. Or by being pulled out of the Fade through tears in reality. It's also establishes that they have a different way of viewing things and they're just as freaked out by the mortal world as mortals are freaked out by the Fade.
- Some spirits might even be able to "become somebody else", which is never really elaborated on too heavily. Cole and possibly Leliana possibly (based on the player's choices in previous games) are two such examples.
- The Legend of Zelda:
- The games have numerous ghost-like spirits. The most famous ones are the Poes, who haunt graveyards and abandoned buildings and carry lanterns which hold their souls, which can broken open to collect the Poe's soul in certain games. Other spirits exist, such as the cyclopean Ghinis, which can turn invisible, and the Hyu, similar to Poes but not as aggressive, and likelier to be found haunting ghost towns and deep forests.
- In The Legend of Zelda: Twilight Princess, humans trapped in the Twilight are turned into spirits, appearing as floating, greenish flames unless Wolf Link uses his enhanced senses, at which point they show as ghostly apparitions.
- In Shining the Holy Ark three good spirits are in charge of magical floating spaceship, the titular Ark. However the Ark gets destroyed so they escape in a pod, crash onto our heroes and possess them. This heals our three main heroes (as they were squashed by the escape pod) and makes sure they can never die, gives them additional powers and allows themselves to heal up while they inhabit their bodies. Meanwhile an evil spirit possesses the King and his advisers in an attempt to revive the 1000 year kingdom and bring fourth an age of darkness.
- In Nasuverse, there are many types of spirits, but they all share common characteristics. Spirits are immaterial existences that "exist with a shape, but without physical properties". Their bodies are described as "Elementals" (Seirei, in the original Japenese), meaning they are conceptual and thus are able travel without physical interference (passing through walls and people, for example).
- Spirits who came from Alaya (collective human unconscious). Mythical beings that exist in human imagination, called "Phantasmal Species". They lack the capability to interact with physical bodies (immaterial) and can't be perceived by humans unless enough people believe in them. If enough humans believe in them, Phantasmal Beasts can become "Divine Spirits", capable of taking material forms and influcencing the World around them with their Authority.
- Spirits who came from Gaia (Ultimate One of the Earth). Nature Spirits that serve as Gaia's extension of will. These can influence physical bodies as they please, and usually packs enough power to wreck reality around them apart at will. The only known example of this are the "True Ancestors".
- The Lower-Class Spirits, or better said, ghosts. Remnants of dead living beings (human, animal, or even plants) that remain attached to the world for some reason. These are immaterial, unstable, temporary existences that have to consume life-force from living beings to continue existing. They can, however, grow so powerful to the point of being able of materializing themselves.
- Finally, there are the Heroic Spirits. Humans who manage to imprint themselves inside Alaya due to their fame as "heroes" in human history (either actual or made-up). Their souls are recorded in the so-called "Throne of Heroes", and their souls can be summoned as Heroic Spirits by Holy Grail, powerful artifact of True Magic capable of manipulating and materializing souls. Heroic Spirits can take material or immaterial form at will, but they need living being's life-force to exist in the world.
- In Avatar: The Last Airbender, the spirits inhabit a Spirit World, but many of them have the ability to take form in the 'real' world, as well. In terms of vulnerability, it varies from spirit to spirit. On the whole, taking form in the real world leaves them vulnerable to attacks, and if they take on a permanent living body, such as the moon and ocean spirits, or the eponymous avatar, they can be permanently killed. Powers also vary: some are a Anthropomorphic Personifications and have abilities linked to that, while others are random assortments. As far as genies, fairies, souls and ghosts are concerned, its kept ambiguous or not really mentioned.
- Captain Planet and the Planeteers features four of them: Gaia (the Spirit of Earth), the eponymous Captain Planet, and their Evil Counterparts Zarm (the Spirit of Destruction) and Captain Pollution, respectively. What they all have in common, is having human forms, and Immortality, at least when speaking of natural causesnote ; otherwise, they can be killed. Nobody ever tried to do this to Zarm, however.
- Speaking of Zarm, he and Gaia may be polar opposites when it comes to their alignment (she's good, he's evil), but they do share some traits and skills, even though Gaia seems to be less willing to use them to the extent Zarm does. They both are Masters of Illusion, can create and control weather phenomena (see their battle in "Summit to Save Earth, Part 1"), and their powers are part of them.
- The two Captains share super-strenght, the ability to fly, hamminess and, uh... specific type of humor. Other than that, they're as different as they can be, even working as each other's Kryptonite Factor.
- Many of the entities call "ghosts" in The Real Ghostbusters and its sequel Extreme Ghostbusters are not exactly disembodied souls of the dead as the traditional depiction of ghosts, but Spirits; entities from another dimension that, as Egon puts it in one episode, "have always been ghosts". Some episodes even show these dimensions. And some of the most dangerous (and of the very few recurrent) villains like Samhain and the Boogie Man are Spirits. In general, Spirits in the Ghostbusters animated universe are basically some sort of normally evil chaotic creature made of ectoplasm and with certain magical powers.