when you read the notes you receive, the'll say you have to strike the hart once with the hammer, then strike it one time with keening (which then should give you an immortal substance, haven't noticed anything though).
then the notes say they will not explain the third step to wield the power from the hart, but instead they say you have to hit the hart several more times to destroy it.
i don't want to destroy the hart, so is there another way or does someone know the third step to wield the power?