Impure Diamond Strike (3.5e Maneuver)

''He recognized the Dance of the Spider stance. Poor move considering what he was about to pull off.''

Make a melee attack. If your opponent has an initiator level, uses maneuvers, or uses maneuver-like abilities, you get +2 to your attack and +6d6 damage. Your opponent must make a DC 15 + Int modifier Fortitude save or fall prone and uncentered. A successful save negates the prone and uncentered effects, but not the extra damage.

If the creature does not possess maneuvers or an initiator level, this strike does not get the bonus to attack, but still gets the bonus damage, and only has a save vs prone.