Ancillary Ordinance is a trait in Destiny 2 that can appear on 15 weapons. An enhanced version exists on crafted and some newer weapons.
What Ancillary Ordinance does
Rapid elemental final blows and final blows on targets affected by elemental debuffs periodically prepare a homing micro-missile, which is launched from your target after this weapon's next final blow. Multiple missiles can be prepared.
Enhanced version
Rapid elemental final blows and final blows on targets affected by elemental debuffs periodically prepare a homing micro-missile, which is launched from your target after this weapon's next final blow. More missiles can be prepared.