Spells are good for farming boys. Lets say that you are about to win but you have 6000 people on their team to go, that's when you would use the 'kill all' spell. It stops you from winning and lets you farm out a couple thousand more before finishing the level. Other than that I don't know what the power or defense ones do...
i won!!! :O F*CK YEAH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!