Storm:

If successful, you may designate five hexes on the battlefield to temporarily become hostile hazardous terrain for the duration of the battle. These hexes must be adjacent to at least one other Storm hex. Increase the number of hexes you may designate by one for every 5 you exceeded the DC. Casting Storm while in another nation's territory raises the complexity of the spell by one tier. Additionally, by increasing the cost of this spell by three, you can grant immunity to damage from the storm to all domestic units.