Your weapon stroke guides your allies, showing them where to focus their attacks.

At-Will   ✦     Arcane, Weapon
Standard Action      Melee weapon

Target: One creature

Attack: Charisma vs. AC

Hit: 1[W] + Charisma modifier damage, and the target takes a -2 penalty to the defense of your choice until the end of your next turn.
Level 21: 2[W] + Charisma modifier damage.

Published in Player's Handbook 2, page(s) 68.