THE POPULOUS BIBLE
C.31 Firestorm
This spell will make fireballs fall from the sky. It can destroy up to four huts and will usually kill - or at least harm - anyone who gets into its path, except your own followers. It also affects Angel of Deaths. Anyone caught in it will, understandably run around in a panic, thus adding to the carnage. A good anti-buildings and anti units/shaman spell.
However firestorm is very ineffective against towers, so it would be unwise to use it against firewarriors sitting in an array of towers.
You will obtain this spell in level 14 and you can store a maximum of 2 shots of it at once.
It's usually used online, but rarely charged until later stages of the game. It's very efficient to clear defenses full of troops so you can walk inside the enemy's base easier.
Note that a shaman can always regain control of herself by casting blast (or other cheap spell), although if she’s still under the line of fire she’ll imediately lose control again. The firestorm area of effect is not regular, and sometimes it's range of fireballs is higher than a player thinks.
Magic shielded units are protected from this spell.