Blood magic can be used in a few ways. First, it can be used to smell or taste the balance of the blood, that is, determine whether a person is a pureblood or changeling, and what race they come from. While a useful skill, it is not limited to the Daoine or Dochas- for example, Cu Sidhe can also smell the balance of the blood. Another way lesser faeries can use blood magic is to mimic the magic of the giver. The spite that Evening Winterrose summoned was able to use her blood to make bargains in her stead for at least a day, for example.
A type of blood magic specific to the Daoine and Dochas is riding the blood, which is the ability to experience what has happened to the dead by tasting the memories in the blood. This magic can be dangerous, because it "skips the brain and goes straight for the gut." It can be extremely unpleasant, since the user will feel the emotions and hear the thoughts of the dead, and the effects can linger. "Riding the blood isn’t an exact art: bits and pieces can linger for days, their secrets shaking loose like sand through a sieve." 
Third type:borrowing abilities