Spellbook of protection

The spellbook of protection provides a useful spell that causes you to glow and decrease your AC by 3, but only temporarily. The spell is best during severe fights with monsters.

A routine to fight a difficult monster might involve:
 * zapping the spell of protection
 * wearing one or two rings of protection
 * switch from non-metal to metal armor

Together, this provides a temporary AC boost, however at least one character was killed by an Angel even after doing this. To fight the most difficult monsters, one must not only have a low AC, but one must also acquire several resistances.