This rare substance is said by some to be the blood of the Crone, goddess of winter and natural death. Others say it is the blood spilled to create a Hand of Glory. It appears to be blood of unusual colour and thickness. It is inevitably found in vials of thick glass.
When placed in a body of water it will cause that water to become fetid and undrinkable. Any guardian spirits of the place will be twisted into evil, sent insane, destroyed, or freed from their connection to the place. It is said that even one drop can contaminate an entire lake, or a river for ten miles.
Crone's Blood is a deadly poison, since it will affect blood. However it is difficult to administer, since all drink and most foods have enough water that Crone's Blood will change their appearance and odour. In any case there are other poisons far cheaper and easier to obtain.