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Vengeful Oath
Ranger Utility 16

Seeing a foe wound one of you allies fills you with vigor and hardens your resolve against the offender.

Trigger: An enemy bloodies your ally or reduces your ally to 0 hit points or fewer

Effect: You can spend a healing surge and can make a saving throw against an effect that a save can end. Using your Hunter's Quarry, you designate the triggering enemy as your quarry.

Vengeful Oath is a daily power available to rangers at the 16th level.[MP2:41]