Blistering outburst
rogue attack 17
Requirement: wielding a light blade.
Target: each creature in burst you can see
Attack: Dexterity vs. Fortitude
Hit: "1[W] + Dexterity modifier damage, and the target takes a −2 penalty to attack rolls until the end of your next turn."[MP:82]
Blistering outburst is an encounter power available to rogues at 17th level.