The Ghost of Faust!

Though now The Yellow King of Daemons and Fallen Dreams, Faust was once man but then ruined by Asphelum Mordeus, or by his less dark name, Asmodeus. Faust sought to create a pact between him and the Daemon to give him all he ever wanted. Asmodeus was a fairer creature then, not as disillusioned by the grandeur of men and women alike as he is now. He bade Faust listen to all his requests and he would grant Faust all he ever wanted.
Faust was keen as the rewards trickled in, but his avarice knew no bounds and from each misdeed, each time he ignored a request and behaved as the spoiled brat he surely was, he bore The charagma into the world: his deeds played upon his flesh as weeds began to grow and burrow into him, turning him ferocious and misshapen. This weed became known as witchweed, and from it, it is said to have bore a beast as full of greed for a full life as himself, a striga. His deeds caused him to burst into flames and wither into Lemuria, where he reigns supreme.
Such then, are what parents tell their children when they misbehave; "You will be possessed by The Ghost of Faust! He'll turn you into a striga, so he won't be alone in that forsaken realm."

Summary

parents have adopted this story to scare their children into behaving by claiming that the ghost of Faust craves to know that he did not displease Asmodeus without right, and he seeks a right of privilege from his own nature. "If all people are like me," the parents translate for their version of Faust, "then Asmodeus was wrong to banish me!" And so, when his realm grows larger than the Ars Materia, he will have proved Asmodeus wrong, all for the sake of his own pride. This works on children that are impressionable but old enough to reason.
Other parents will take the story in a different direction for their younger ones. The Ghost of Faust, they say, is deterred by clean places, or places where a craft is displayed, which is why farmlands are typically safe. So for those who don't do their chores, he will come in, sleep in the house where there are shadows to conceal him, then begin to steal things, then jump into the most evil person in the house, and make them sick with greed wanting for things they cannot have. If you are thought to be possessed by the Ghost of Faust, the person must be shut in an empty room. Of course, this is what is told to the child in a very serious manner, however, there have been families that are zealous enough to go through with it, giving some merit behind the story.
Due to these families, there are odd circulated cures for being possessed by the Ghost of Faust: such as, "You must walk along in the woods at night and be attacked by an animal. Only then will he leave." Or, a personal favorite of most who don't take the story seriously, "You must walk out into a thunderstorm and be struck twice by lightening, once for exorcism, twice for good measure."

Historical Basis

Faust is an illusive figure in history, but is noted as a scientist of The Old Ones. He is thought to have either co-created The Iron-Gier with another engineer, or have created the charagma as a bioweapon. Whatever the case, there are not enough documents to prove this.

Variations & Mutation

Instead of focusing on Faust at all, some tell the story of a striga, a ghost that lays dormant in people that is woken up by misdeeds. In other tales it is an extra soul a person is born with that is unlike a Conduit and will fight for control in a person causing them to become barbaric and malicious.