Life's/Death's Edge (3.5e Sacrifice)
From D&D Wiki
The Gate channeled the power of life and death, and through it's cycle, comes energy, the energy to live. By controlling the flow of positive or negative energy you produce a baneful edge around your weapon. As a swift action, your attacks deal either 1d6 negative energy or 1d6 positive energy in addition to normal effects. Positive energy only has effect on undead, and cannot be used to heal. The effect lasts for 1 round.
Health Cost: -3.