Corona

Once per combat encounter, you can free-cast Blindness/Deafness. This will not count against your spells selected/prepared, and does not use up a spell slot when cast. It uses the spell save for your own spells.

This feat is for spell-casters only, and must have their INT, CHA or WIS equal to 14 or above. In addition, spell-casters who take this feat must be over level 10.