Greater Spell Focus
Choose a school of magic, such as Evocation or Illusion, for which you have already selected the Spell Focus feat. Your spells of that school are even more potent than normal.
Prerequisites: Spell Focus, caster level 6.
Benefit: Add +2 to the Difficulty Class for all saving throws against spells from the focused school of magic you select. This overlaps (does not stack) with the bonus from Spell Focus (see below).
Special: You can gain this feat multiple times. Its effects do not stack with itself. Each time you take the feat, it applies to a new school of magic.