Balefire

After one turn of preparation, a bar of pure light emits from your hand forming a line 100 feet long and 10 feet wide that launches out from you in a direction you choose. Each creature in the line must make a Dexterity saving throw of a DC 22. A creature is instantly killed and an object is instantly destroyed, and its existence is wiped entirely from time on a failed save, the spell has no effect on a successful save. During the preparation round, a creature may succeed on a DC 15 insight or arcana check to see if you are preparing the spell. If you take damage during the preparation round, make a concentration saving throw.