Sauromantian Soothsayers: are they there exclusively to feed my evil blood rituals?

[Wrana]

Yes, good idea. There was Baalz' guide on communions somewhere. This goes under his category of "reverse communion", I believe. He also mentions that as individual buffs affect all slaves, you can use Light of a Northern Star and Power of the Spheres to make all slaves S3. Then you can spam whatever you want with them, reinvigorating periodically. I would probably prefer Enaries for such a communion, but you can just take your cheap researchers and make a fighting force of them at any moment.