Piercing Arrow (transmutation)

Don’t make an attack roll for the attack. Instead, arrow fires forward in a 1 ft wide, 30 ft long line. The arrow passes harmlessly through objects, ignoring cover. Each creature in line attempts a Dexterity saving throw.
•Failed save: creature takes damage as if hit by
the arrow, plus extra 1d6 piercing damage.
•Successful save: 1/2 damage. The piercing
damage increases to 2d6 at 18th level.