WIP: This page is on a very initial state and still needs lots of work from being organized to lots of rewriting.
There is a huge array of possible creatures living, surviving and even thriving inside it. There are creatures that look like things and things that look like creatures. There are creatures that look like anything and nothing at all. Anything that can and is imagined can be imagined as having any property and one of such properties is being alive, so anything at all can be alive in the Imaginarium.
They remain undamaged by their surroundings because that is the way they have been imagined and they are very stable for the same reason. After they have been imagined in such a way, their own reality gives them the stability needed to resist such environment. and the abilities needed to navigate it. Even then their eventual deaths can still be attributed to the corruption inherent to the environment.
Many of the creatures from the Imaginarium crave the property of being real and are uncontrollably, sometimes even unconsciously, drawn to it. Many do hunt and prey on anyone or anything real they can find to feed on such property. Being a victim of such an attack causes one to have that property drained away. This is a similar effect as the inherent corruption of the environment, except that it is directed, focused and much faster and obvious. The creatures doing it gain the absorbed property and are able to become partially or even fully real themselves in return, at least temporarily.
Some use this to then enter Imaginatas and continue their existence in there, usually as heralds of destruction in some way because they can never be fully real no matter what. A rare few are able to become well adapted inside some Imaginata, and find a role to play in there with a live for themselves. They are, almost always, mythical, magical and mysterious characters, never being able to fully integrate themselves on normal societies and pass as a normal person.
Many beliefs about gods and similar entities are probably legends about such creatures. That is possible the reason of the somewhat common belief that gods need worship to keep their power or even that they are subject to the beliefs of their followers. The requirement for belief can be explained by such entities slowly and slightly feeding on the imaginations and wills of those directing their thoughts to them and the belief that they are subjected to the beliefs of their followers points to a possible subjective nature of such entities which would be plausible for a, at least partially, unreal entity originating from the Imaginarium.
They can never find some way to become fully real because the flow of reality is always on the other direction through the corrupting effect of the Imaginarium. Even Imaginatas slowly decay into fiction and unreality. Even if it is possible to counter this and gain or recover some amount of reality, one can never fully reverse the process and, once partially non-real, it is never possible again to be fully real again. A part of unreality, no matter how small, always remains.
A few of such creatures are even sapient.
Those are then able to continue to imagine themselves in order to enhance their survival. Such entities can shape their surroundings by focusing their minds and become very powerful within such realms for they imagine themselves and their realms that way. They can even become god-like in their realms if they are able to focus their minds enough. Some have encompassed entire Imaginatas inside their realms making them the rulers of such worlds. There is even a theory that such entities could have imagined themselves into being. In the areas of the Imaginarium where there is no causality, time or similar limitations they certainly could and some probably have done just so.
Despite this the Imaginarium itself has no ruling entity over its entirety. Some entities can be perceived that way due to them ruling a large enough area but there are always many other areas outside of their realm. This is just a special case of the Imaginarium having no global rules or properties.
In their essence, all these beings, sapient or otherwise, are just another form of Imaginata, for they are the creations of imagination.
Types of Creatures
The idea of being alive itself or the idea of creature are some easy examples for ideas that easily became alive by themselves inside the Imaginarium. It is very easy for other ideas to merge with those, possibly through some accidental collision, possible by directed action from some entity, giving form to some more complex idea that is also alive.
Some ideas or things have been imagined as being real. This creates an inherent contradiction for they are imagined things being imagined as real things. This results in half-real, half-fictional things left to roam the Imaginarium on their own. They are called Thought Lurkers.
There are some native creatures to the Imaginarium, basically because they have been imagined to exist. In the same way that the ancient sailors imagined monsters on the deep, far away and unexplored seas, so have those who ventured into the Imaginarium imagined great and fantastic monsters living in it.
Sirens are a type of creature that appears as the greatest dreams and desires of anyone interacting with them in order to allure them to their deaths. Before consuming their entire victims and their inner reality they turn into the ugliest nightmares of their victims.
Others, instead, feed on the will and/or ability to imagine that normal creatures possess, leaving behind only mindless husks incapable of new thoughts at all. Not all feed exactly the same way so their victims can end up with many different symptoms. They then use these abilities to empower themselves, spending all the willpower and imagination they have consumed in the process.
Trappers capture the minds of their victims to slowly feed on them, not touching the bodies at all. The bodies of the victims can even be taken back to reality or have never left. Such victims will remain with their minds trapped inside their fantasies, unable to relate with, perceive or interact with reality in any way. During this time their thoughts and mental energies are slowly being drained and sucked away by swarms of these things until there is nothing left and the body ends up dying as a vegetable. These creatures usually find it easier to attack and entrap those who enter the Imaginarium in their minds alone instead of physically and so they prefer such targets.
The victims of the corruption of the Imaginarium, which where once real but no longer are, remain there as fictional living creatures like the ghosts of past explorers. At least those who have the will to keep themselves going after their change into unreality, that is. They have been unmade and now continuously search for some way of being made real again.
Some of the most dangerous creatures of the Imaginarium have such hungers that they feed directly on entire Imaginatas, bringing destruction to their inner Cosmologies all at once like great beasts of the Armageddon.
FixIts are ideas that attach themselves to the minds of those able to have ideas of their own. They cause their victims to become progressively unable to think of anything other than the idea attaching itself to them. As their victims devote more and more of their willpower and mental energy to that specific idea it slowly grows and becomes more powerful. It digs its tendrils deeper and deeper into its mind's brain and mind making it progressively harder for them to think of anything else until they are fully consumed by that single thought and there is no space in their mind for anything else. Sometimes a small number of these ideas join together in symbiotic relationships, having the entire group attach themselves to a single victim or sharing multiple victims. This allows the victims to focus on all the ideas in the group instead of a single one, allowing their minds to function just a little better, which increases their life expectancy. All the ideas in the group share the mental energies being drained from the target so, if there is a single target, they get a smaller share but the groups do tend to allow for a higher probability of being able to feed. On very rare occasions, the victim embraces the idea being forced into their mind and make themselves into something like an Avatar of that idea. By doing so and freely dedicating much of their brainpower to the idea attached to them they retain much of their freedom of thought in order to better support the idea in question, being able to thing any ideas capable of directly or indirectly support it or any ideas needed to act in ways that benefit it. They also sometimes act in ways designed to capture more victims for the idea or for the ideas joined with it on a symbiotic group. An example of one such avatars was a philosopher monk who got devoted to the idea of conquest and become one of the worst warlords on his world.
Some creatures that present themselves like genies, offering to turn the target's greatest fantasies into reality in exchange for some emotion or memory or similar things. They drain some part of their victims mind that way, removing specific memories or making them unable to feel the drained emotion again. They can also take away some particular thoughts, etc. They don't actually turn the target's fantasies into reality, instead they call them from the Imaginarium and make them appear to the target, looking real. As time goes by and the target slowly stops fantasizing about them and feeding them with their continuous thoughts they start to fade away until they are completely gone.
Some stories told again and again have never been much developed beyond their core aspects. They happen in very limited settings which have never been developed or imagined beyond what was needed for the story. These stories continue to loop repeatedly in very small half-formed Imaginatas that are much less resistant to the influence of the Imaginarium around them because of it. Sometimes the characters in these stories start to became aware of their situations, getting glimpses of repeating situations of events. Eventually they can begin to understand their realities as prisons and try to escape. It is usually easier for characters considered evil to gain this awareness of their situation because such stories usually have a morality and commonly end with the evil characters loosing in some way. The inherent suffering of such loss repeated times and times again is a very powerful factor in the awakening the awareness of their situation. The normal consequence of becoming aware of it is that they try to escape what they see as their prisons. This can be done by reshaping their small worlds to allow them to leave which requires them to be able to counter the willpower of all the accumulated imagination of all those who told and retold their stories. Another apparently much easier way to escape is to find someone with whom to trade places, entrapping the victim in their place and role to continue to relive the story in their place.
The spirits of the death from those Imaginatas where the dead go through the Great Barrier into the Imaginarium. They are condemned to roam in there for all time, slowly fading away as they are forgotten by the living in their worlds. As all that remembered someone who had died slowly join them in death, their spirits are remembered only by the spirits of the more recently deceased and so on. Like ideas thought out by other ideas , they become figments of figments of figments as they slowly fade away. Some of these forgotten spirits will do anything to be remembered again.
Idea Virus are virus that infect the minds of their victims and start changing all their ideas into that single idea. That is how they reproduce, each idea that is modified becomes a new identical idea virus. Their victims become single minded and obsessed with the idea as everything they think about turns into it.
Other type of Djinn occur from thoughts and desires so strong that they become crystallized and assume a physical form, capable of persisting even outside of the Imaginarium.
Imagination elementals, they are not made of imagined things but made of actual imagination itself. Different types of imagination energies that have condensed into living creatures.
The creatures in the Imaginarium have no absolute limits to what or how powerful they can be. It is possible to find god like creatures in there more powerful than any entity that can be found inside any Cosmology of any Imaginata. This is because the structure given by a Cosmology always imposes some kind of limit but in the Imaginarium, there is no such thing, only freedom. Pure, raw and unlimited potential. The only real limit would be in the case of the possibility that an absolute creator god really does exist. In that case its power would be absolute even over anything and everything that could exist even in the deeper parts of the Imaginarium. But even then, more powerful creatures could exist in there, it's just that even those would fall under its power in an unavoidable contradiction. In the same way that the Box contains all the things larger than itself and all the things that contain itself.
Psychic Vampires are a type of creature that feeds on specific types of mental energies, depending on their own specific tastes. Some can drain certain types of thoughts, feed on specific ideas but usually they survive by feeding on emotions. Many feed on desires and what would be considered to be sins and they take the traditional roles of devils by enticing their victims to indulge in activities which increase the related emotions so that they can feed even more. Another example would be a creature trying to keep some personal fantasy alive as its own personal world but unable to do so by itself so feeding on similar thoughts of others in order to maintain it.