In a multiplayer team game, there might be ways to pay N mana and get N+1 demons to benefit from your Unholy Blood Ritual. For instance, you could quickcast UBR, then full cast a demon, and then your teammate could cast [mwcard=MW1I23]Rouse the Beast[/mwcard] on your demon, which would get to benefit from UBR even though you didn't pay the damage cost for that demon. At least, I think this would work, but I don't have UBR on me right now and I can't find it online (without watching a youtube video).
But in general, if you think of your remaining life as a resource, then UBR is just a [mwcard=MW1I03]Call of the Wild[/mwcard] with a variable cost that is paid with a different resource.