Spellcasting Acolyte

This feat gives the ability to cast unprepared spells from your spell book or repertoire at a -10% chance, per spell level, of success. If successful doing so will use up the equivalent level spell slot. If unsuccessful, that will be the end of your action. For example, casting an unprepared level one spell will use a level one spell slot but at a -10% chance of success. Casting a level 9 unprepared spell will have a -90% chance of being cast successfully. If unsuccessful a spell slot is not consumed.