Personal headcanon time, discretion and a saltshaker advised:
We've established that the Voidsent are drawn to corpses and death - There was another thread that covered this pretty well and there's dialogue from 1.0 that may or may not be retconned that infers that not taking proper care of a dead body can cause it to rise as a Revenant.
I don't think "blood magic" or "void magic" are things. I do think, though, that the Voidsent on the Other Side can use blood to find a way through the barrier into our realm. In the case of demon wall, it's less that a blood ritual manifests the wall into a monster and more than a voidsent is able to crawl through into our world thanks to the nature of blood. Dealing with Voidsent is basically providing them a foothold to step into our dimension; Edda wasn't raising Avere, but she was doing a great job of letting a proto-ahriman take over what was left of his head. The similarity is too much to be coincidence (for my money, anyway).
We've established that the Voidsent are drawn to corpses and death - There was another thread that covered this pretty well and there's dialogue from 1.0 that may or may not be retconned that infers that not taking proper care of a dead body can cause it to rise as a Revenant.
I don't think "blood magic" or "void magic" are things. I do think, though, that the Voidsent on the Other Side can use blood to find a way through the barrier into our realm. In the case of demon wall, it's less that a blood ritual manifests the wall into a monster and more than a voidsent is able to crawl through into our world thanks to the nature of blood. Dealing with Voidsent is basically providing them a foothold to step into our dimension; Edda wasn't raising Avere, but she was doing a great job of letting a proto-ahriman take over what was left of his head. The similarity is too much to be coincidence (for my money, anyway).