SPELL_STONESKIN

Usage       : cast stone skin
Accumulative: -
Duration    : Level of caster
Level       : Level 18 current class mage only
Mana Usage  : 12

Modifies casters AC by (level * 2), rounded down to the nearest 5. Thus,
at level 18, it reduces AC by -35, and at 31, by -60.
Characters of classes other than mage will notice a difficulty moving with
this spell cast on them. Since they do not have as keen a grasp on the
magic involved, the transformation takes a toll on their body.