The blood of such an individual possessing this Power has very special properties. Cut yourself, bleed out a few drops, and you can Shape the blood into a creature of your desire. This creature will have a measure of your own powers. So, for example, if you have the Blood of Amber, your blood creature will have a bit of power over Pattern as well.
Corwin’s ‘blood bird’ is a prime example of a creature made of Shape Shifted blood. In this case the bird has the power to fly through Shadow and has an innate “homing” connection to Corwin. It’s also important to note that the blood bird is a non-player character. It operated independently of Corwin, delivering Oberon’s package, then leaving, then returning to rescue Corwin at that moment when his life was in grave danger.