You excel at picking apart an opponent's defenses when your allies also threaten him.
Martial
Combat Reflexes
Adaptable Flanker
When an ally and you threaten an opponent together, you can treat that opponent as flanked. You gain a +4 bonus on your attack rolls when flanking.
You and your ally must be on the other side of the opponent to flank. Flanking grants a +2 bonus on attack rolls.