Target must succeed on a DC 12 Fortitude save or suffer a -2 penalty to its To Hit attempts for the duration of combat. The -2 To Hit penalty applies to all attacks the victim makes, not just ones directed at the caster of this spell.
This effect does not stack. Therefore, the bane effect is not augmented by multiple castings. The effect from this spell does not stack with the effect from a Cloak of Curses.