Heroes of Nirmathas
This thick green snot-like substance was first seen oozing from the face of a recently raised undead wolf. Some of it sprayed on Der Tiger’s fur and Magar’s beard, instantly turning both gray and slightly brittle.
Next, the unknown man near Grey Lake seemed to have collapsed on an alchemical jar that contained some of this ichor. The fabric of his cloak under the broken jar appeared much older than the rest of his clothing. Under the cloak was severe necrotic damage.
Finally, after fighting the ancient skeletons the familiar, sickening smell was encountered and a dried green dust was found on the old bones.