Marksman's Rhythm fires on projectile hit. On a piece that carries it it reads: Projectile hits build Rhythm: +{value}% Projectile Damage per stack up to {count}, fading 3 s after your last hit.

Word for word it is Projectile hits build Rhythm: +{value}% Projectile Damage per stack up to {count}, fading 3 s after your last hit, and the number in it grows with the gear: 1 to start, 0.02 more for every item level, and it only goes off every 15 times you set it up.

0 bases carry it.