Simply Irresistible

You find it easier than most to be able to tell what a person's physical and mental limits are, and have modified your magic to push those limits. Chose one school of magic (transmutation, illusion, enchantment, necromancy, evocation, divination, abjuration, conjuration). Proficiency Bonus times per day, you can add +2 to the next Spell Save DC of the chosen school, at the cost of -2 to Spell Attack for 1 minute.