Arrow Storm

Arrow Storm deals 4 damage to any target.
Raid — If you attacked this turn, instead Arrow Storm deals 5 damage to that permanent or player and the damage can't be prevented.

The List

Khans of Tarkir

Arrow Storm deals 4 damage to target creature or player.
Raid — If you attacked with a creature this turn, instead Arrow Storm deals 5 damage to that creature or player and the damage can't be prevented.

Raid abilities care only that you attacked with a creature. It doesn’t matter how many creatures you attacked with, or which opponent or planeswalker controlled by an opponent those creatures attacked.

Raid abilities evaluate the entire turn to see if you attacked with a creature. That creature doesn’t have to still be on the battlefield. Similarly, the player or planeswalker it attacked doesn’t have to still be in the game or on the battlefield, respectively.