The most useful spell.

I really like the Plague faction; if you take the Pain Lord, it helps me a lot until more complex spells are learned. Phantom is very useful against neutral creatures when you have a couple of stacks of ranged units or units that deal damage without taking damage in return. Divine Retribution is simply overpowered. Under the right conditions, the damage from this spell is just insane. I like Berserk more than Subjugation, although I don't know why. And even though no one has mentioned it, Heavenly Shield shouldn't be underestimated either.