[Ragnarok-X]

im playing a game as pangea lately and im using a bit of bloodmagic as well, though just for summoning, not for battle. My tactic to get JUST enough bloodslaves is to to get approx 3-4 Pandemoniacs, they have nature 3, blood 2. Send every pan in a different provine with approx 2-4k population and let them hunt for 1 or 2 turns, just so you get 15 slaves. Put the tax to 70 % (it wont make a difference income-wise anyway, since the provine only gives 20 or so at 100%) Now let each forge one rod and continue to hunt. Now You should get approx 15+ slaves per turn.
Of course this wont be enough income if you rely on blood magic, but its enough for some fiends of darkness or dark vines.

hope i helped you.