Sacrifice is a basic ability, one of three abilities released with the second world event, The Bird and the Beast. It was purchasable at the event with 21,000 renown and a gold event token, and requires level 10 Constitution to use. Now the event is over, it can be obtained as a very rare drop from General Graardor and Kree'arra. When received as a drop from the generals, it is automatically learned; it does not drop as an item. When received as a drop, the message You have unlocked the Sacrifice ability! appears in the chatbox.
When Sacrifice is used, the player deals up to 100% weapon damage to their target regardless of protection prayers, and is healed by 25% of the damage dealt, or 100% if the ability kills the target.
Sacrifice is a basic ability. Unlike other basic constitution abilities, it does generate adrenaline.
While training Combat, it may be helpful to time your hits so that you heal a good amount of HP from using this ability. Wait until your opponent is relatively close to dying, then use the ability. Do not use it too early or too late; otherwise only a negligible amount will be healed.