Blood Magic

Blood magic is as simple as it sounds; the use of blood to bolster other magical abilities. It is not an art that many people learn for two primary reasons;

The first reason is that the magic is addictive, at least according to any accounts from practitioners that can be believed. A calling, an itch, a need to kill more and more to use more and more blood for greater and greater power. No recorded or otherwise known practitioner has been able to resist this once they move past using their own blood or that of small creatures, and after that point they become dangerous to everyone and everything around them.

The second reason ties to the first. Because those who practice blood magic are almost always universally dangerous at the first signs it's being practiced most societies turn on the casters, seeing them imprisoned or killed to save themselves from the danger that the caster could eventually present.

Still, there are those who practice the art but they do so in understandable secrecy. They know they will not be understood, and if they operate in the bounds of normal society they tend to mask their use of blood magic with other types of magic or store the blood and pass them off as potions to those who ask. Sad that such an art must be so hidden, though given the power that it can give to those who choose to practice it is highly unlikely the knowledge will ever truly die out for good. Yet also understandable, for power corrupts and there is no greater power than holding the life of another living being in ones hands and watching the light in their eyes go out as their blood fuels even greater magics.