Curse of the beast lord/Princes of hell.
This is an exceeding rare item that the party found in the Challenge Tower. After some research, they identified it as a substance with properties that can bring people back from the dead (under the condition that it is used near immediately upon that person’s death). It was put to the test when Gabrielle died while fighting Nagas in the dungeon that Silverlight (see other entry) was found. Sebastian smashed the phial on her dead body and she immediately woke up.