"You ever heard of the Sangre tribe? Miracle healers from the distant lands of the Gnoll? Of course not, as news from that place seldom traverses the sea.
Those who belong to it are indoctrinated into the cult of their goddess, patron of healing, so basically all of them are trained medics and alchemists. Once in a while, the goddess bestows her gift to a newborn, focusing the entirety of the baby's healing power on one side of their body. This results in the so-called "Miracle Blood" from the tribe, able to heal all mundane and magical illnesses, given the appropriate treatment.
How do you think they treat those babies? As prophets, perhaps? As Kings? No, they are simple blood bags for those savages, permanently secured to a wooden chair and forced to bleed continuously while fed raw meat to replenish their precious blood. But there is a catch: because of the so-called blessing, the other side's blood is highly poisonous, capable of killing a weakened creature on the spot.
Turns out a pathogen infected their water supply, and they needed blood. And turns out the only one able to harvest it from the miracle-granted Gnoll was the village idiot, not able to tell right from left. You can figure out the rest of the story, right? They got what they deserved, if you ask me.
Anyway, I really got to go, but it was a nice chat, you know? Next time, educate yourself on your target's history before hunting them, and think twice before drinking from their canteen. Except you won't have a 'next time'. Cool weapon, though, mind if I take it? Would be a waste to let it rust out there."