You make one of your spells affect multiple targets.
Benefit: A mass spell changes a spell with a range of touch or close that has one target into a spell that affects multiple targets. The range of the mass spell becomes close (25 ft + 5 ft/2 levels), and the target becomes one creature/level, no two of which can be more than 30 ft apart. Spells that do not have a range of touch or close, spells with a target of you, and spells that have more than one target cannot be affected by this feat. A mass spell uses up a slot four levels higher than the spell's actual level.