A vampire can shape-shift to many forms, since they are gifted with supernatural strength and deceptive powers. The common belief that vampires can only shape-shift into a bat is obsolete when you have the power of strength and speed, do you want to be just a bat? Vampires can deceive natural senses, it is their prerogative to choose any kind of animal form unless there are laws that bound them to forbid. Since vampires refrain from being seen because of the fear of being exposed, shape shifting is the best way not to be recognized in open places, especially at nighttime. An animal that is not too dangerous to roam around society is a wise choice to be around ordinary people. Who cares if there is a dog, a cat, or a bird roaming around?
As vampires continue to exist from generation to generation, their knowledge are up to date. They witness the transition in every era of human development, when you live long enough, you become smarter, and wiser in living among with human beings. You cannot be dumb forever, even time could improve that flaw. The fear of vampires has subsided because of factual explanations of science, but there are still silent people who believe in them. If it is true by chance, then vampires are doing quite well in disguising themselves as humans. Who could unravel further secrets about them? Assumptions can only be made based on the narrative from the past.
The weaknesses that drive them away have something to do with their absence, like sunlight, these bloodsuckers cannot go out during daytime. Susceptible of pain when they get closer with onions or garlic, unbelievable. What seems to be harmless to ordinary people become the most dangerous thing for them. If these monsters transform into friendly pets, distancing from what people eat on the table is necessary, to avoid foods with onions or garlic that is potentially harmful for them. Just imagining how awful would that be in their part, and how bizarre in our perspective, when a cat suddenly acquire sore eyes, burning skin or any adverse effects that vampires have. There were religious beliefs that say holy water may burn their thin skin because it is sacred, and it consists some sort of spell that could extinguish evil spirits too.
All these possible counter-attacks for vampires are applicable only in land battles, however there were no records in history where these monsters transformed to be aquatic animals. Their lives would be endangered, since the ocean has potential predators for them, plus vampires cannot breathe underwater, and their powers are minimized. What would be the reason to go underwater? In some cases possible, if their prey escaped and hid in the water. We do not know what more they can do, but this assumption should not be final. If we limit their transformation base on terrestrial habituation for the reason that vampires exist in land, then we can explain their transformation of being a bat, when these bloodsuckers have no wings in their normal form.
Vampires are extraordinary creatures who possess the gift of immortality which grants youthful appearance. A privilege that contributes to their long-lasting lives without being threatened, if vampires can look like us, there are no reasons to worry unless caught in the act of being a vampire. It is interesting to imagine the kind of lifestyle they have, living with us. Vampires live long enough to see the major events in every generation, more knowledgeable than a thousand human beings combined. All the power they possess, including shape shifting, are too great to be true. When a normal person possesses this power, there is no doubt that he will abuse it for pleasure. Vampires could be notorious lawbreakers with their supernatural strength, they could rob a bank or kill a person and get away with such crime.
For pleasure, vampires may transform into mosquitoes to stalk their crushes, or pretend to be someone with their youthful appearance. Vampires can do a million of crazy ways to mess up with ordinary people, even if you can abuse such power, there is no guarantee that you can live a happy life. You cannot build a connection with human beings that would equate to the same span of a lifetime.