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Hunter's Teamwork
Ranger Attack 1

You use a nearby ally to gain advantage with your attack.

Ranged weapon

Target: One creature

Attack: Dexterity vs. AC
Effect: If two or more allies are adjacent to the target, you gain combat advantage against the target with the attack.

Hit: 1[W] + Dexterity modifier damage.
Increase damage to 2[W] + Dexterity modifier at 21st level.

Hunter's Teamwork is an at-will power available to rangers at the 1st level.[PHH1:MH1]