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Unerring shot
rogue attack 17

Requirement: wielding a crossbow, a light blade, or a sling.

Target: one creature

Attack: Dexterity vs. AC

Hit: "3[W] + Dexterity modifier damage."
Miss: You do not expend this power if you were hidden from the target when you made the attack.[MP2:67]

Unerring shot is an encounter power available to rogues at 17th level.