Format:
cast 'armor' <target>                   cost:  8 mana
cast 'shield'                           cost: 18 mana
cast 'displacement'                     cost: 24 mana

   The above three spells all subract from your ac, or armor class. The lower
your ac the better armored you are.  The better armored you are, the less
average damage you will take during a fight.

'armor' affects ac by -20
'shield' affects ac by -30
'displacement' affects ac by -40