I just handed one of these out in my Doom & Tea Parties campaign, so I figured it’s time to put it up here.
The bloodthirsty swords are rumored to be 27 bronze scimitars fashioned by a coven of rakshasa mothers for their eldest children, sons and daughters, to wield in battle as they carved their paths with pain and death in the world. They tend to sport bone or wire-wrapped grips and bear odd, stripe-like striations along the dull edge of the blade, or down at the forte, just above the hilt.
The blades are not sentient, but wielders report that possess a certain animal intelligence. They whine or vibrate unhappily when chopping into undead, or other bloodless enemies, but sing and strike true when used against living creatures. Against non-living foes, they are +1 blades that do the usual damage. Against the living, they are far more potent.
In addition to conveying a +2 bonus to the attacks of their wielder, a true strike can be utterly devastating to the foe as the blade drinks greedily of their blood. For damage, roll two dice: a d20 and a d4. Divide the result of the d20 by the number that come up on the d4 (rounding up to 1 when necessary).
If the blade goes longer than a week without being used against a living creature in combat, it will begin to hunger. Anytime an attack roll results in a 1 there is a 50% chance the blade will twist in the hand of its wielder and bite into a living ally (no additional roll is needed; just go straight to the damage roll). The blade can be sated for a time with domesticated animals (pigs, goats, geese, etc) but will eventually tire of such mawkish fare. After a month of such a diet, the sword will do its best to be stolen (attracting the attention of thieves and murderers) or lost so that it can find its way into the hands of a more adventuresome warrior.