Blackrazor

Blackrazor, also known as the Sword of Souls, is a greatsword that appears to be forged from an unknown alloy of steel. It is sheathed in a black scabbard decorated with pieces of cut obsidian. When held, it shines like the night sky filled with stars. The wielder of the sword hears faint whispers whenever it delivers the killing stroke to a living creature. The sword has a sentient being of another plane of existence forced into it. This creature was once a powerful undead creature similar to an atropal.

Blackrazor in Baldur's Gate II
"Ye who hold the razor's blade

Forged of darkest iron

Quenched by blood and fear,

Know that ye hold the key

To the one who guards

Bhaal's sacred murdered tear."

- The genie's riddle

Blackrazor is a longsword with powerful enchantments but an evil nature. It is offered to the protagonist of the game in the test of greed in the Pocket Plane near the end of Baldur's Gate II: Shadows of Amn. They may either choose to use it to kill an enslaved genie guarding one of the Tears of Bhaal and keep it, benefitting from its power especially if and when their story continues in Baldur's Gate II: Throne of Bhaal, or choose to relinquish it, avoiding a fight and passing the test in the "good" way.

Blackrazor has a +3 enhancement bonus, and when wielded grants regeneration and immunity to Charm and Fear effects. It has a chance with each hit to drain the target's life force (levels) and convert it into healing energy and a temporary boost of speed and strength for the wielder.

Trivia
The sword Blackrazor was also part of the adventure White Plume Mountain. The sword was an intelligent and chaotic neutral blade that encouraged its wielder to kill indiscriminately, eagerly devouring the souls of those it slew.