A blood spear was a type of weapon blessed with Vampiric necromancy magic. Originally no different than a mundane spear, a blood weapon would gain magical properties through the actions of its wielder. Great warriors who would drink the blood of their prey and keep their weapon stained with blood occasionally found that the weapon would respond to their violence. Over time, they could invoke magic to a transfer a creature's life force once killed. In doing so, they would gain temporary sustenance, allowing them to fight for extremely long amounts of time.
Blood weapons had a limited sentience, generally invoked by the spirit of their former owners. When wielded by someone that the weapon did not favour, they would not be as effective in combat as when wielded by their chosen kind.