[Bananadine]

Well below Evocation 9: Grip of Winter, Heat from Hell, Rigor Mortis, Foul Vapors. Only the last is reliably deadly on its own, but all can incapacitate or kill large armies pretty cheaply, if you can hold off the enemy while they do their work... and if you can prevent your own side from being significantly harmed.

Summoning a bunch of elementals can be a good way to hold off the enemy for a while (or even for the rest of the battle, if you spend enough gems on it).