Greater Ringing Weapon
Bard Attack 27
A great clap of thunder accompanies your strike, which seems to linger on your enemy, calling your allies' attention to your foe's position.
Special
Trigger: You hit an enemy with a basic attack using a weapon.
Effect: The enemy you hit takes 15 thunder damage. Until the end of your next turn, that enemy grants combat advantage and cannot benefit from partial concealment.
Greater Ringing Weapon is an encounter power available to bards at the 27th level.[HotF:68]