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Flattening shot
rogue attack 3

Requirement: wielding a sling

Target: one creature

Attack: Dexterity vs. AC

Hit: "2[W] + Dexterity modifier damage, and you push the target 1 square and knock it prone.
Cunning Sneak: The attack deals extra damage equal to your Intelligence modifier."[MP2:60]

Flattening shot is an encounter power available to rogues at 3rd level.