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

Encounter   ✦     Arcane, Weapon
Standard Action      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.

Published in Player's Handbook 2, page(s) 73.