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From pebble to boulder
rogue attack 27

Requirement: wielding a sling.

Target: one creature

Attack: Dexterity vs. Fortitude

Hit: "2[W] + Dexterity modifier damage, and you knock the target prone. The target is stunned until the end of your next turn."[MP2:70]

From pebble to boulder is an encounter power available to rogues at 27th level.