How to use blood magic effectively in battles?

[Velusion]

Micah said:
L4L is B3, but only 1 slave, so a B2 mage could get a cast off...not exactly "above average" there. He'll be very much KO'd from it, but L4L is kind of a multiple-caster spell anyhow if you're trying to drop a 200HP SC.

I'm pretty sure the computer won't cast it (it will default to something else) unless you have 3B. I've actually been testing it out in test games the last few days and I can't get the B2 mages to cast it (even when loaded up on slaves).