To put it simply, Vagairies are like elves or fey, if they were also Missingno.
They are the psychic run-off of humanity; living dreams that could have perhaps been gods if they were more coherent, more convincing of the lie that they are real. Instead, they are the stillborn failures of mankind's dreams and wishes. They command great spiritual power and wisdom, but are simply unable to properly use it as they should. They're the autistic savant children of Divine.
Imagine if you will a spirit born out of the world, made of entirely random, unrelated concepts of Men's Dreaming. An empty suit of armor with a stocky, masculine form stands, a floating cyberpunk mohawk crowning the hollow space above the chestplace. It speaks in a helium-like young child's voice, and it refuses to budge, demanding water and that it has enough sun. A warrior-a-rebel-a-child-a-plant; scrambled and assorted madly. Perhaps it doesn't have the concept of self-preservation; many of their kind were such, entire generations of their ilk merely stood and allowed themselves to be slaughtered.
For they are persecuted by the Church. The Church. That Church. Your Church. Any Church. They are parasite embryo gods that siphon off faith merely by interacting with mortals, sustaining themselves as a prolonged dream and distracting them from full-hearted devotion. And no god wants to see these things rise up to their level. It's not that Vagairies are particularly more wicked or dangerous than other creatures, but that their ascension undermines faith in the Gods themselves.
Because Vagairies are less than even humans. Their souls are nubs and karnels. Sparks of ash compared to the burning candles. All of them lack of a core, fundamental aspect of what it means to be human in their psyche. A Vagairy that does not love is not one that simply does not fall in love but in fact literally cannot feel it. A Vagairy with no sense of self might mistake the rumors he hears as his own thoughts and opinions, and never be able to vocalize an original statement of belief or intent.
In exchange for these handicaps, they command great power. While they will not be loved by gods, they have a psychic insight greater than any other kind of creature; they were born from the sea of the unconscious, after all. And beyond that, they were born directly of the womb of the Earth, and may command the world. The samurai-plant-child above, for instance, might always have the sun, because they defined themselves as always having enough. Perhaps it is always daylight within their line of sight. At any hour of the day, or when hidden from the sky. Perhaps our rumormonger who cannot tell his thoughts from hearsay can hear every rumor in the world, and knows all secrets that have been shared with another.
And there are those that can actually pass for human. The ones that can hide their natures, conceal their flaws, and pass themselves off as children of gods.
There is nothing that will not be more cursed by Heaven and all under its dominion than such a child, no matter how sincerely innocent.
Below is the generalities of playing a Vagairy, but do note that exceptions to every rule exist, by design.
Advance: As Elves
Saves, HD, To-Hit, etc: As Pseudo-Class
Ability Scores: Vagairies are especially in tune with the world, but have weak egos. If you use Ability Score Racial Modifiers, give +2 Wisdom and -2 Charisma; if you use Requirements, they should have a Wisdom of atleast 13 and a Charisma of no more than 12.
Vagairies can advance in a single class of their choice in a similar way to how Elves emulate Fighters and Magic-Users. They cannot be Clerics, or any other class that functions due to being in the good graces of a god (rarely, a god may accept a Vagairy, though they usually encourage their natural gifts instead of giving them divine empowerment). This is an attempt at the Vagairy to fill the missing part of themselves, as Vagairies are not, and cannot ever be, true people. Pick a major portion of human experiences; the Vagairy can never experience or comprehend it. Examples could be never knowing love or being loved, being incapable of forming long-term memory, having no self-preservation instinct, or even no concept of being an individual separate from what they observe. They might even lack major 'flaws', like being incapable of hatred. This list is not exhaustive, and it should be sufficiently debilitating in their impersonation of people.
Vagairies have no souls, and thus cast no shadows and are immune to anything that requires it, including Raise Dead; they are like Elves in this way, except they even lack their lower spirits. In exchange, they each have a type of limited instrusive telepathic insight into the people around them. Perhaps they can smell relationships and thus know who's associated with who, or perhaps they know every rumor about a person (without knowing truth from lies). Perhaps they can quote the last thing your mother ever said to you, or sing your favorite song from your memory. It should always be mono-focused in this way, and played to eerie effect; Vagairies have this ability because they do not understand the walls between people; they come from the soul-sea underneath the people-islands in the collective consciousness.
At 2nd level, and every level thereafter until Name Level, a Vagairy gains another Power, but gains another Ban. Powers can replicate spell-effects, or be more esoteric. Good examples include things like a cat-form that can return from the dead nine times in exchange for her memories, or the ability to command a single type of monster in exchange for taking their weaknesses from them. Bans are rules that a Vagairy can never deny or break, such as never being able to handle man-made items, enter homes or churches, or be above ground during a sunset or sunrise. If a Ban is broken, the Vagairy loses access to its corresponding Power for atleast as long as it broke the Ban, plus a day per level.
At Name Level, a Vagairy has stepped closer into the realm of humans. They may choose to cast a shadow and repress their bans and powers, and gain the half-souls of elves. They can start gathering followers as a member of their Pseudo-class, but they must repress their true nature to them unless they are a fanatically loyal follower. They also gain a quasi-immortality, such as being unable to die under the light of the moon, or always returning to life three days after their death if mourned for by a virgin that loved them.