Dracocyps
This fungus can only survive in alpha dragon species, and even then, the host needs to feed off other dragons to keep the fungus alive. In exchange, the fungus adds the DNA of the dragons consumed to the hosts so they are able to hunt more efficiently hunt. Dracocyps is spread by the host reproducing so it increases the host's fertility but this doesn't always work so sprouts will grow under the tongue and release spores as the host breaths, expanding the range of hosts to take root in.
Night Furies are the most common carriers of this fungus as they prey on other dragons anyway.
Dracocyps has a unique effect on them. The saliva of a night fury allows the fungus to survive outside the host's body for limited amounts of time, resulting in it turning the tongue into a reverse lure targeted at humans. No one is certain why exactly they developed this technique of scaring away humans with a fake corpse but it is effective as witnesses begged to never have to go where they saw them again. It has been discovered that these night furies possess the same intelligence as humans if not more. The fact that they can mimic voices means that it's only a matter of time before they find a way to blend in with humans. While not hostile to humans they hold grudges and will take revenge when given the chance.
So if you see a woman in a white dress with long black hair that looks like she starved in the cold, take care not to do anything that could be seen as a threat.
If for whatever reason you have to go through night fury territory, throw your weapon away. You may not be able to see them, but they can definitely see you. If you find your weapon by the door, they are asking for a favor.