Dark Angel Aphasia

Dark Angel Aphasia, also known as Contagious Global Aphasia, is an Abyssal illness that gradually destroys the ability of its victims to communicate, even telepathically, even as they develop an instinctive knowledge of the Abyss. In its final stages, it destroys the mind utterly, absorbs the victim into the Abyss, or occasionally spontaneously vanishes with no long term effect, but with the victim being completely amnesiac of all the time he was infected.

Overview
Dark Angel Aphasia is a thing of incredibly mysterious origins, even its name; recently infected individuals often have dreams of a beautiful, eldritch being always described as an "angel" made of the night sky. However it first entered the world, it now exists as a sort of toxic meme; the Mysterium theorizes that the fundamentally indescribable nature of the Abyss is the core reason why the gulmoth manifests as aphasia; as the victim develops an ever more acute and accurate knowledge of the void, she loses the ability to describe her newfound wisdom in any comprehensible way. Until a victim cannot communicate, however, enough can be gleaned from her increasingly garbled but understandable speech and writing that it serves Dark Angel Aphasia's vector.

Infection
A potential victim of Dark Angel Aphasia is exposed to it by conversing with a Stage 1 victim about the Abyss or studying her creative works. Aphasics are driven to explain their newfound insight into the Mystery of the Void to everyone around them, and listening to them (or reading their books) provides tantalizing insights into the Abyss that a potential victim invariably grows obsessed with. The obsession is in fact the initial stages of the aphasia, despite the fact it cannot be detected magically except as a mundane obsession; if the infected is isolated from the victim or the diseased work in question for three days, or shows the strength of will to break free from the obsession, the infection fails and the would-be victim realizes he was acting irrationally (because the actual knowledge of the Abyss does not vanish though, many mystagogues are obsessed with collecting Dark Angel works to study in a controlled environment). Should the potential victim keep up their study, however, the aphasia fully imprints itself on his mind and they progress to Stage 1.

Stage 1
The most virulent stage, but also the only chance to treat the victim, Stage 1 manifests as increasing insights into the nature of the Abyss, but also the progressively worse inability to communicate that gives Dark Angel Aphasia its name. The Stage 1 victim begins to suffer from minor errors in writing or verbal speech first, followed soon by the other. As the aphasia progresses, the victim becomes increasingly desperate to communicate his growing insight into the Abyss and into the nature of magic, but as the disease advances, both writing and speech become increasingly garbled rambling. Over the course of about four to five weeks, the victim grows increasingly incomprehensible in both forms of communication (assuming the infection isn't stalled for some reason), until both become little more than random arrangements of nouns and verbs. Treating at this stage requires that the victim be refocused on the living world rather than the Abyss; through psychology, and possibly Mind magic to help with communication, the victim can be gradually guided into thinking about his mundane life and non-Abyssal topics; if the victim stops obsessing over them, the flow of unclean insights ceases, and he regains his language. Otherwise a mage can use powerful Mind spells to forcefully remove the aphasia, but this method also leaves a permanent susceptibility to further infections.

Stage 2
The terminal stage; at this point psychologically or even magically treating the victim is impossible, as neither he nor the uninfected can understand each other. His words and writings seem suffused with meaning, but nobody else can parse them (this does mean that they are no longer vectors for the infection, though). At this point, all anyone can do is pray; in four to five days, the victim will lapse into a coma, at which point one of three things will happen:
 * Three-quarters of the time, the victim has an apparent seizure, at which point his mind vanishes, apparently absorbed by whatever entity the dark angel is. While it appears to be a vegetative state, in fact all traces of the patient have vanished, even memories; the thing left behind is just a living shell only good for having a new mind implanted.
 * 12% of the time, the body vanishes too; as soon as nobody is looking, all mechanical devices observing the patient spontaneously glitch, and when the image resumes, all trace of the victim is gone.
 * The lucky remainder has a full and spontaneous recovery from the coma, with any and all symptoms of the Dark Angel Aphasia gone. The victim is completely amnesiac from the point of his infection to the recovery, but otherwise perfectly fine and mentally sound. Mages theorize this is the result of an attempted absorption by the Abyss, but somehow the victim rejected the blending and the Abyss rejected him in turn.