Black Sap

Black sap is a sludgey tar like substance produced by the unnatural decay of world trees. Over time, it hardens into black amber and is rendered harmless.
The elemental composition of black sap is extremely volitile and unbalanced. Contact with living creatures disrupts the elemental composition of the body, rejecting the soul; essentially inflicting a form of Zombification upon them.

Manifestation

Black sap leaks from the between the bark of a world tree that has been killed through unnatural means. It smells sickly sweet, like decay. Once enough of the sap beads on the bark, it will roll down the tree and settle into the soil.

Localization

Black sap only manifests in world trees. Other trees affected by the same corruptive forces do not exhibit the phenomenon.