AFAIK = As Far As I Know,
There are some other somewhat similar spells, I believe, though I don't remember which ones are quite like that. Deadly stuff.
Blood slaves are easier to use in battle when your units don't set them on fire with their heat auras...
I have had good results with battlefield blood as Mictlan. Some of the spells are quite potent but can be tricky to use properly.
PvK