Shape-Changing
Although there was a small link between shape-changing and vampires for hundreds of years, it was not until Dracula that the true connection was made. In the novel, Stoker described Dracula as able to change into a rat, a bat, or the very mist itself.
Vampire bats became by far the most common of these shapes a vampire could command at will. This could be because vampire bats, by their nature, are closely related to the vampire itself. They are nocturnal, and feed exclusively off the blood of various mammals and other vertebrates. They have very sharp teeth which they use to pierce the victim's skin, and then they lap up the blood as it flows. It has also been known as an emerging problem; it is a proficient carrier of rabies (not unlike the definition of Nosferatu, which itself mean plague-carrier).
The ability to transform at will into mist has brought many advantages to the vampire, allowing him to escape vampire hunters and other dangers quickly. In addition, mist (in some cases) has allowed the vampire to move great distances at one time.