Blood Magic is a rare and mysterious yet powerful ability that exists in the world of Game of Thrones.
Elsera Snow has considerable skill at blood magic. In the source books, it is most often yielded by Melisandre, who has yet to appear or be mentioned in the Telltale game.
Blood magic is strongly reliant on actual sacrifices of blood and lives to empower it. For that reason, its practicioners are often seen with reservations and mistrust. Blood of a King or of his offspring is claimed by Melisandre to be particularly powerful.