Vicious Offensive is a 1st level Fighter At-Will power. It was introduced in Dark Sun Campaign Setting.
Vicious Offensive
Fighter Attack 1
You smash into your opponent with such force that a nearby enemy can’t help but take notice.
At-Will ✦ martial, weapon
Melee weapon
Target: One creature
Attack: Strength vs AC
Hit: 1[W] + Strength modifier damage, and you mark an enemy adjacent to you until the end of your next turn.
Level 21: Increase the damage to 2[W] + Strength modifier damage.