HoMM IV Reference Guide.

If there are vampires and other monsters in the army, then when one vampire is lost, you can cast Sacrifice on another unit – there will be more vampires than the initial number, but they will remain even after the battle. In this way, you can significantly increase the number of vampires by using random monsters. Really? Added after 34 minutes Order magic is valuable primarily at higher levels. But it is difficult to level up two strong mages at once. The combination of Hypnosis + Sacrifice is a very powerful combination. This is also incorrect.