Defining a Fear
In general, defining a Fear is easy to do based on what a Fear isn't rather than what it is. This is mainly due to the fact that Fears represents hundreds of different traits and rarely coincide with one another in physical or mental behavior. However, a few traits due tend to pop up.
1. Most Fears are either nearly impervious or entirely invincible to any damage.
2. Fears often induce violent insanity in victims whom either interact with or are attacked by them.
3. Fears appear to be immortal.
Even with these guidelines, this leaves a lot of grey area when really discussing what a Fear is. As such, there can be heavy debate between what is a super-human monstrosity, and what is an actual full-blown Fear.
A Fear does have one major definition by name, and that it it appears to be a manifestation of some kind of terror, phobia, or "Fear" (as it were) that afflicts mankind. As such, a Fear is always known as the "Fear of X", which for example The Pendulum is the "Fear of Time". While the definition of what the Fear is will typically satiate standard human curiosity, it is worth noting that the "Fear of Time" is extremely general, and only barely explains what The Pendulum can do and has done, which can be said for nearly every Fear.
As a mock example, a "Fear of Darkness" does not necessarily require the absence of light, but may be capable of manifesting its powers in low-lit areas, cupboards and dressers, closets, and even small containers, anywhere where the term "darkness" can be explained, including inside the human body or under clothing.
It is also worth noting that these labels are of human design and are used to understand these being in human terms, something that they often violate. Some sentient Fears have adapted these labels to themselves, although whether they identify as the "Fear of X" isn't entirely certain.
Fears are not benevolent, but not all Fears are malevolent either. The Reveler for example isn't entirely malevolent, but by his behavior causes extreme damage. The Pale Maiden is hardly caring of who it interacts with, extending its damage as it travels, but not specifically aiming for nor attacking individuals whom do not harm it. The Burning Bride is malevolent and directly harms people.
Fears do often resemble humans, but it isn't certain why this is, as Fears are not human. That being said, it is highly debated if Fears have always existed, or Fears only exist because of humans themselves. Since Fears of the fears of humans incarnate, it is possible that such beings would have never existed without humans, as proposed by some anti-Fear sentiments.
Many Fears often have churches or cults that follow their teachings, however the involvement of the Fear is entirely up to their temperament. Some, such as the Burning Bride, require people to become her servants through pain. Other Fears, such as The Pendulum, have absolutely no interaction with their cult that formed on its own and perpetuates its own existence. Others still, such as those following The Reveler, will join into his situation willingly without understanding or caring about the consequences.
Obviously, the exact definition of what constitutes a "Fear" is not agreed upon by all. While some may see The Nightlanders as being a Fear in their own right, others may simply see them as being the servant-victims of The Empty City. The most common consensus among those who are aware of Fears generally follows Optic Nerve's PRE system.
Fears have no collective prescribed behavior, and vary heavily in their decisions. In addition to this, no two Fears get along well enough to share territory (except in the rare case of two or more entities who embody one Fear, which is still technically one Fear).
Views on life, humanity, Earth, and so forth are often highly varied. Some entities, such as The Reveler, see humanity more or less as toys, The Pendulum is entirely indifferent to sentient life altogether, and The Burning Bride doesn't particularly like any living organisms that aren't under her control. As a result of these beliefs towards humans, their decisions and actions never directly coincide. For this reason, Fears will typically go out of their way to purposefully avoid entire situations that will cause them to come into direct conflict with other Fears, whether it's out of respect, honoring an unknown code, or just worry of a battle.
The only typically agreed upon function that Fears follow is The Great Game, which isn't well understood. Theories have been proposed that its existence is little more than a way for Fears to intimidate humans, while others propose it isn't able to be understood by humans as to its goals, rules, terms, or how to determine victors.
It is known that sentient speaking Fears do reference knowledge, theology, and statements that typically sound either malevolent or completely alien in their concepts. What is written down by Fears cannot be read by humans unless written in human languages. Reading the philosophy of a Fear in the language of the Fears often results in madness, as Fears are understood not to "speak" or "write" in the general concept of what a human would call "speaking" or "writing".
List of Fears
The Cold Boy - Fear of Isolation and Cold
The Plague Doctor - Fear of Disease and Medicine
EAT - Fear of Obsession and Water
The Pale Maiden - Fear of Loss
Project NEWBORN - Fear of Technology
The Grotesque - Fear of Sleep and Dreams