Sapphire Nightmare Blade p. 65
Your study your enemy for a brief moment, watching his defensive maneuvers and making a strike timed to take advantage of a lull in his vigilance.
The sapphire nightmare blade is one of the most basic, but important, maneuvers that a Diamond Mind adept studies. It illustrates that a keen mind can pierce even the toughest defenses.
You attempt a Concentration check as part of this maneuver, using the target creature's AC as the DC of the check. You then make a single melee attack against your target. The attack is also part of this maneuver. If your Concentration check succeeds, the target is flat-footed against your attack, and you deal an extra 1d6 points of damage. If your check fails, your attack is made with a -2 penalty and deals normal damage.