What are your favorite battlefield spells?

[Maraxus]

Sometimes you need a bigger gun - sometimes you need Gift from Heavens.

Other then that, I like Soul Vortex, because it makes the Wraith Lord a small, nice army-killer.

[Humakty]

Thunder strike is real good for two reasons I think : low research cost, and the boost all air mages get to precision. The only flaw is the high fatigue. For long battles I tend to think FFs are better, even if you never really know were it will land.(fire mage are usually old, and this impacts greatly precision)
The best casters not using gems are for me dragon anathemants : FF spamming with no risk to kill your troops.