Nightblade

The Nightblade is a black dagger made of adamantine. It has a onyx gem on its hilt. In addition to the following abilities, the Nightblade is a +1 Adamantine Dagger.
*The Nightblade adjusts itself to any alignment or substance requried to overcome damage reduction. This attunement lasts for 1d4 minutes after the last time it made contact with the appropriate creature.
*A creature hit by the Nightblade looses 2 hp / round for five rounds.
*The Nightblade's weilder feeds on her own vengance. For every 10 points of damage the weilder deals in a given round while holding the blade, he gains a +1 luck bonus on attack rolls, saving throws, and skill checks made in the following 5 rounds. If the weilder is in a Rage (as the barbarian class feature), this changes to a +2 luck bonus per 5 points of damage.
*If the wearer speaks a command word, the blade of Nightblade becomes pure shadowstuff. If the weilder makes a touch attack with the weapon in this form, the subject's heart stops. The subject suddenly drops to –8 hit points, then –9 hit points at the end of this round. If someone immediately makes a successful Heal check (DC 15) or somehow gives the subject more hit points, she stabilizes. Otherwise, at the end of the next round, the subject reaches –10 hit points and dies. As this attack leaves no wounds, it appears as if subject died naturally (assuming the weilder didn't attack him in any other way). A Fortitude DC 15 check negates the effect.
CL 20th; Craft Magical Arms and Armor; vampiric touch, sadism, stop heart; creation must take place on the Plane of Shadow; 200,000 gp.