Death magic of prognostication. Since the near-dead are said to be able to see beyond the veil, and some older cultures would divine the future by reading the offal of sacrificial victims, mash together to get a society that uses sacrifice to tell the future, but it is verbally transmitted (instead of reading "signs"). Could throw in a good deal of old Oracle speech (often in myth, the Oracle is thought to have said one thing when in fact only in hind sight predicted the opposite, not to mention that Oracles had interpreters to make sense of their babbling). So the culture brings the sacrificial victim to death's door to have them tell the future.
Are the sacrificial victims telling the truth, or are they lying to screw over the people killing them? Is there a way to compel the victim to disclose specific information, you know, other than seeing Gramps welcoming them home? Could someone be kept at the edge of death to continue to give advice? Do you kill them, and then somehow get them to talk in a Max the Miracle Worker way? What does that kind of magic do to the practitioners and society?
Just a wild larking idea.