Bloodthirsty

Bloodthirsty — a magical weapon with this property grants a +2 bonus to attack rolls and to a single damage die of weapon damage if, and only if, the weapon dealt the killing blow to a foe with at least four hit dice within the past twenty-four hours. Otherwise, it imposes a penalty of two instead of the aforementioned bonus. These Bloodthirsty modifiers are in addition to any other magical bonuses the weapon possesses. Thus, a +3 Bloodthirsty shortsword might provide an overall bonus of +5 to to-hit rolls and to a single weapon damage die.