Source: Book of Spirits p147
This Numen allows the spirit to inject its opponent with a form of spiritual venom after a successful blow or bite, causing damage and befouling its enemy’s own reserve of spiritual energy. After a successful strike in hand-to-hand combat, the spirit may spend one to three points of Essence to inject a supernatural venom into its foe. The venom inflicts an additional point of damage for every point of Essence spent. In addition, the victim must succeed at a Stamina roll, or lose one point of Essence for each point of Essence the spirit spent. This corrupting effect also works on other forms of supernatural energy, though to lesser extent. A target that doesn’t use Essence will lose only one point of his reservoir to the spirit-venom, no matter how much Essence the spirit spent.