D&D4 Wiki
Merciless cut
rogue attack 19

Requirement: wielding a light blade.
Effect: Before the attack, you shift your speed.

Target: one creature

Attack: Dexterity vs. Reflex

Hit: "4[W] + Dexterity modifier damage, and ongoing 10 damage (save ends)."[MP2:68]

Merciless cut is a daily power available to rogues at 19th level.