This was original for a Cleric that worships a God of war... Such as Tempus or Bane. It can be used for an evil character or carefully by a Good aligned character (as long as they are not Lawful Good).
Cleric Weapon: Hammer of Blood
This weapon appears to be a magical +2 to hit weapon, once identified or attuned the follow properties reveal themselves to you.
Drawing first Blood - When any enemy gets to 50% of their health (or Bloodied status) the hammer senses the blood of its enemy and increases to +3 weapon.The Blood of my Enemy, Feeds me - During any battle encounter, after drawing first blood you may declare one of those bloodied enemies as your chosen enemy, and upon a successful strike, you will do an additional 1d8 points of damage, and each round following that you stand alive, the chosen enemy will take that bleeding damage until they are healed. You may use this …