Ritual Dagger: Sacrifice the Victim

You can select a victim for a terrible ritual. If a victim gives their consent, they will die, and you will gain the First Action effect that increases damage dealt or healing from the first spell by 500%.
This spell can be cast only in the Observatory raid adventure or on an Astral allod.
Action Toy(with additional properties)
With the victim's consent, kills them and applies a ghostly effect to you that increases your damage dealt and incoming healing for the duration of one spell.
Source: kill Ath-Zak in the Observatory adventure on high difficulty.