What is the wording on Piercing Arrow? Where it is from?Sneak Attack
Beginning at 1st level, you know how to strike subtly and exploit a foeís distraction. Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.
You donít need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isnít incapacitated, and you donít have disadvantage on the attack roll.
The amount of the extra damage increases as you gain levels in this class, as shown in the Sneak Attack column of the Rogue table.
I don't see the word attack here, hit by arrow is not hit by attack.Piercing Arrow
You use transmutation magic to give your arrow an ethereal quality. When you use this option, you donít make an attack roll for the attack. Instead, the arrow shoots forward in a line, which is 1 foot wide and 30 feet long, before disappearing. The arrow passes harmlessly through objects, ignoring cover. Each creature in that line must make a Dexterity saving throw. On a failed save, a creature takes damage as if it were hit by the arrow, plus an extra 1d6 piercing damage. On a successful save, a target takes half as much damage.
The piercing damage increases to 2d6 when you reach 18th level in this class.
I don't think you can get SA at all.