The AtG Missile Mk. 1 is a returning item in Risk of Rain 2. It gives the player a 10% chance to launch a rocket that deals 300% total damage every time an attack connects with an enemy. Total damage is equivalent to the specific amount of damage dealt by an attack, meaning that if the player deals 100 damage on an attack which procs a missile, the resulting projectile will deal 300 damage to the enemy it hits. The rocket fired unfortunately does not deal splash damage, however to make up for this it locks onto the nearest enemy and chases it down until it dies or the rocket connects. The chance to trigger is multiplied by the Proc Coefficient.
This item is extremely powerful on almost any character when stacked, especially characters with high single-shot damage such as Loader and Huntress with Ballista equipped, as the damage for the rocket is calculated based upon the damage dealt in one hit. As for lower damage but higher DPS characters like MUL-T with the Auto-Nailgun or Sawblade equipped, it is best to save this item for characters who can use it more effectively.