Waif

Waifs are a danger to travelers known to virtually all cultures on Yvari. Most describe them as girls or women who look as if they had simply fallen on hard times - emaciated, often bruised. Their stories are heartbreaking - abusive parents or step-parents, an abusive lord with the girl herself being an orphan, or accusations of her being a witch and her village casting her out.
Regardless, if the traveling group decides to take her in - waifs don't approach people traveling alone - somehow, inexplicable, tensions in the group will start to rise. Sometimes it will be related to the new girl, other times it will be seemingly random. Any tensions that had been there before will slowly intensify.
Over time, the girl will recover and slowly start to look like a healthy human again, despite eating surprisingly little. Travelers paying close attention may realize she does not eat at all, since waifs are unable to eat human food. Instead, they feed on drama caused by conflict between others - the more intense, the more nourishment they gain. People being able to reign in their emotions are best protected against waifs, but they will still be tested.
In the worst case, an all-out brawl will break out with the travelers murdering each other. Even if there are survivors, the waif will have disappeared after the brawl, since they got all they could out of them.
Few, if any, people are aware that waifs may not be necessarily restricted to the female form or even restricted to feeding off travelers. Some scholars in the Eye of Magic theorize that every community has one of these people - the old hag or the intolerable old man constantly stirring up trouble are just examples. Even animals could be affected, according to this theory. They suspect goats, donkeys or cats to be especially likely to be waifs, though some also believe that rabid foxes are, in fact waifs.
Especially the last point contradicts folk knowledge of waifs and is hotly debated among the few scholars specialized in waifs. Proponents of the theory dismissively wave folk knowledge away, since common folks can't possibly be taken as reliable sources. Their opponents point out that so far, all information about waifs - even the fact that they prey on conflict between humans - comes from common folk. Often, they ask the old maid serving one of them to contribute what she has heard on the streets or from other servants, and, strangely enough, just when everything seems to come to a conclusion, she brings in a piece of information that upsets the whole theory, and the heated discussion starts anew, with old Mirella quietly watching.