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]