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Harmony of the Two
Bard Attack 13

As you strike your foe, a nearby ally lashes out with an attack in harmony with yours.

Melee weapon

Target: One creature

Attack: Charisma vs. AC

Hit: 2[W] + Charisma modifier damage. An ally within 2 squares of you can make a basic attack against the target as a free action.

Harmony of the Two is an encounter power available to bards at 13th level.[PH2:73]