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Thundering Spell (Metamagic)
You can conjure your spells into existence with blaring thunder or fearful shrieks, deafening creatures damaged by their effects.
Benefit: You can modify a spell to deafen a creature damaged by the spell. When a creature takes damage from this spell, it becomes deafened for a number of rounds equal to the original level of the spell. If the spell allows a saving throw, a successful save negates the deafening effect. If the spell does not allow a save, the target can make a Fortitude save to negate the deafening effect. If the spell effect also causes the creature to become deafened, the duration of this metamagic effect is added to the duration of the spell. A thundering spell uses up a spell slot two levels higher than the spell's actual level.
Spells that do not inflict damage do not benefit from this feat.