A Phoenix
The wondrous bird is about 18 feet long with a sleek, feathered body that dances with bright flames.
The phoenix is a natural predator of the Elemental Plane. From birth to death, he spends his life hunting through the air. In fact, he lacks any legs that might enable him to land. Even after death he often rises again from his own ashes to continue the hunt.
The phoenix is the most powerful spell a Blood Mage can cast. The idea of a creature rising from its own ashes can also symbolize the blood elves who rose from the ashes of the slaughtered high elves. Thus the phoenix serves as an essential symbol of the blood elf race.
Powerful Blood Mages, like Kael'thas, can summon phoenixes.