Entropy

Entropy is an enchanted short sword +2 which can only be wielded by Tieflings. The only tiefling available to the party is Haer'Dalis, who has this weapon in his possession when joining the party in Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition. If he was not a party member at the end of Shadows of Amn, he has the weapon when he joins in Baldur's Gate II: Throne of Bhaal. The sword inflicts 1d6 +2 points of damage and if the target fails a save, probably vs. death, the weapon will inflict three points of poison damage. It has a THAC0 of -2, a speed factor of 0 and it weighs 2 lbs.

In-game description
"Entropy This +2 abyssal greensteel blade is one of Haer'Dalis' favorite weapons. This shortsword is capable of inflicting an additional three points of poison damage if the target fails a saving throw. This blade may only be used by tieflings."