Adaptable flanker
rogue utility 2
Requirement: an enemy is adjacent to both the user and an ally of the user
Effect: "You gain combat advantage against the enemy until the start of your next turn."[MP:74]
Adaptable flanker is an utility encounter power available to rogues at 2nd level.
Character optimization forums rate this as average, as it gains combat advantage when you normally wouldn't get access to it.[Charop rogue]