Cosmos: Spirits and Demons

Spirits and demons are magical entities that occur throughout the World of Othe.
While the interactions that they have with people vary greatly, they are capable of acquiring power that extends beyond what would normally be in the purview of mortals.
Some powerful spirits are referred to or revered as gods, especially in the ancestor worship that is found in some parts of Othenar and Roltam.
The distinction between a spirit and a demon is often a vague one. While it is not uncommon to hear of lay people describing the difference being that spirits can be good and demons are always evil, the reality is somewhat more nuanced.
Spirits and demons draw their powers from the world, much in the same way as occultists do, though there are key distinctions.
Each spirit and demon is a distinct entity. They have different levels of development: they can be incredibly simple or fully intelligent. More intelligent spirits and demons also have greater abilities, though the power that they require to manifest is increased. Both are known to lie dormant, using only part of full potential until they have enough power to fully manifest.

Types of Spirits

Spirits can draw power from almost any force found throughout the world.
Ancestor spirits are powered by worship, similarly to how New Gods gather their power, but there are key distinctions. An ancestor spirit is limited to gathering power from a very specific set of followers; typically a particular bloodline. The counter-part to this is that an ancestor spirit can be much more powerful than New Gods. As with entropic spirits, ancestor spirits are often the spiritual remains of a formerly living mortal, though they tend to maintain more of their personality and are not formed by necromantic rituals.
Blood spirits are often confused with demons, because of how similar they are: both are fueled by mortal sacrifice. Evil blood spirits demand mortal sacrifice, but unlike demons a blood spirit can form a symbiotic bond with mortals. When this occurs, the mortal makes small sacrifices, typically using ritual implements, of blood or flesh (sometimes scarification is sufficient to satiate the spirit). The spirit is empowered and renewed by these sacrifices and renders aid to the mortal in return. Blood spirits can occur spontaneously, but they are usually created through special rituals, such as those used in the Empire of Egrondest.
Entropic spirits consume natural energy, and are relatively common. They can be identified by leaving a chill or dark spot behind when they manifest, but this is not always obvious. While typically created from mortal spirits as a result of a necromantic ritual, entropic spirits can occur spontaneously. Exotic entropic spirits include shadows, which consume light around them, and gremoi, which feed off of the flow of time. Some entropic spirits are vulnerable to overloading themselves, leading to uncontrollable power and potential dissolution of the spirit.
Nature spirits are tied to a particular natural site or phenomenon. Great beasts and flora may have an associated spirit, with the general guiding principle being that nature spirits do not typically align themselves with intelligent beings, though they may select mortals to be the object of their protection or wrath on the basis of how their actions impact the site or phenomenon that gives them power. Special terms exist for each of the nature spirits, and they can vary greatly due to the fact that their powers are an extension of their source. Elementals are special nature spirits that tie themselves to power sources that could be consumed by elemental spirits, like muses, which are powerred by song (especially spellsong), and typhoons, which are powered by raging oceans.

Demons

Demons are less varied in their nature than spirits, though many will try to disguise themselves as spirits to avoid detection by mortals. Demons are powered by mortal suffering or decay, and surround themselves with it.
While demons are typically evil, this is more of a manifestation of their needs, rather than a personal desire. They may honor deals they make with mortals or do other typically good acts, albeit with the caveat that they will eventually need to be satiated by destruction (voluntary or not). Unlike blood spirits, demons have a difficult time entering into a symbiotic relationship; entering into a bond with a demon causes corruption, so while a mortal can provide a demon with succor voluntarily without sacrificing lives, corrupt mortals provide less sustenance for demons (or blood spirits), and will eventually require either more followers or the demon-follower to sacrifice other mortals by force.
Demons desire nothing more than the power to pursue incarnation and further manifestation: the reasons for this are unclear but the common consensus among scholars is that they are essentially spirits who once defied the Primordials, and as a result are condemned to endless suffering. Manifestation relieves this suffering. Demons who are asked about their nature give inconsistent answers, though whether this is because they are not of the same nature or because they intend to deceive mortals is unclear.

Manifestation

Spirits and demons manifest in three primary ways: incarnation, possession, and projection.
When such a being manifests it must use power that it has gained to pay the price of entering the world from whichever realm it comes from.
Incarnated spirits and demons take on a physical form. This is the most expensive of the types of manifestation to carry out, but once the entity manifests in physical form it consumes less power to remain in the world (and will not automatically be banished when it runs out of power, though it will not have access to most of its abilities). Incarnated entities are resistant to banishment, another advantage provided over possession and projection. Both spirits and demons prefer particular forms, but they have a control over how they incarnate: humanoids and large creatures are more expensive, while bestial and small creatures are more simple forms for incarnation.
In many cases, incarnate spirits' forms merely resemble, rather than replicate, an inspiration, meaning that they are not susceptible to some of the vulnerabilities and weaknesses of that form (but, likewise, may not gain its benefits).
Possession is another way in which entities can manifest. Similar to manifestation, possession uses an existing host as a vessel for the entity. This is less expensive in terms of power. The more powerful the vessel, the more difficult it is for the entity to possess it, unless it is willing. Corruption makes possession by demons much easier, though it has no impact on most spirits (or, in some cases, can prevent a spirit from possessing a host, especially ancestor spirits). Possession is stable unless a host tries to fight the entity or banishment occurs.
Hostile possession does occur, especially if the vessel has been weakened through corruption, rituals, alchemical concoctions, or physical ordeal. It is also possible for a vessel to be coerced or deceived into submission to an entity, though this does not necessarily prevent the vessel from rejecting the spirit or demon later.
Projection is the most frequent form of spirit manifestation, though it is somewhat less common among demons. The entity manifests as a semi-real presence and is able to exert its will. Since every spirit or demon is capable of using magic, albeit sometimes in a very limited fashion, a projecting entity makes itself a physical presence only to the degree needed to cast a spell; usually a vague incorporeal form, with additional sensory phenomena witnessed as a result of mortals' latent supernatural perception. These phenomena match the nature of the entity (a ghostly apparition for an ancestor spirit, leaves for a nature spirit, sulfur and fire for demons, and so forth), and usually resemble whatever an entity's preferred form for incarnation is.