Your fiercely-honed bow training has given way to an incredible technique.
Once per turn, when you make an attack using a bow, you can nock two arrows instead of one.
Make an attack roll for each arrow. If either attack roll does not meet the AC of the target, both arrows miss. If both attacks hit, roll damage for both arrows as if you had made two separate attacks.
You do not add your ability modifier to the second arrow's damage, unless that modifier is negative.