Backstab
rogue utility
Trigger: You make an attack roll against an enemy within 5 squares of you using a basic attack with a weapon. The enemy must be granting combat advantage to you.
Effect: "You gain a +3 power bonus to the attack roll, and the enemy takes 1d6 extra damage if the attack hits.
Level 7 2d6 extra damage
Level 17 3d6 extra damage
Level 27 4d6 extra damage"[HotFL:175]
Backstab is an encounter power granted to thieves by the Backstab class feature at 1st level.