
Transforms the imbiber, granting their attacks and spells a chance to cause additional Nature damage to the Darkmaster and his minions. Duration 1 hour.
You can get the empty vial by killing Professor Slate in Scholomance and filling-up the vial by clicking the potion on the table.
From my understanding, if someone kills your character while you have this buff active, they can also get infected by the same buff.