Blood magic, first and foremost, is the practice of using blood—life itself—as a potent fuel for casting spells. This life may be supplied by either the mage or sacrifices, whether willing or unwilling. Ancient lore and present-day events hint that blood magic holds the key to incredible powers yet undreamed of, or long thought lost. Such power generally requires a terrible sacrifice, however: a debt paid in blood at the cost of the lives of others or the blood mage; or even one's own humanity. As such, while blood magic itself is merely a tool, it is by far the most dangerous means to any end in the realm of Thedas.