Gloom Razor( Tome of Battle: The Book of Nine Swords, p. 35)
The teachings of the Shadow Hand discipline allow you to confuse your enemies. Your attacks and parries are infused with the stuff of shadow. Through careful training and discipline, you learn to use your ki to inhibit a foe's fighting ability with your shadowy nature.
The Gloom Razor feat enables the use of three tactical options.
Lingering Gloom: To use this option, your opponent must miss you due to concealment. On your next turn, you can make a Hide check opposed by your foe's Spot check as a swift action. If this check succeeds, you gain the benefit of an invisibility spell against that foe until the end of your turn.
Moving Shadows: To use this option, you must deal damage to an enemy with a melee attack and move at least 10 feet during your turn. On your next turn, you can treat that enemy as flat-footed against the first melee attack you make in that round.
Shadow Slip: To use this option, you must make a successful melee attack against an opponent you flank. On your next turn, you can make a DC 20 Tumble check if you are adjacent to your foe. If this check succeeds, as a free action you can move to any square adjacent to your opponent without provoking attacks of opportunity from any opponent.