This fascinating being originates from the Philippines. While it is mythological, it is the most predominately talked about and the most feared being for many of the people in this country. There are about five sub-types of this creature, so ill give you a rundown of the most common ideas and characteristics, without confusing you about different types.
This creature appears mostly human, it is often seen to have a combination of vampiric and undead elements. they are also shape shifters and Self segmentaters.
A shape shifter can change their physical/visual appearance at will to fit in with their surroundings, often they pretend to be ordinary people. Although of course at night, they no-longer look human. When they are in their natural form, they are said to have large wings that protrude from their backs, have long tongues that are very thin (proboscis like), they look much paler, bonier and generally barbaric. It is also said they often turn into animals such as dogs, pigs and birds at night. Overall, they are though to be beautiful women by day and incomprehensible horrors by night. A Self Segmentater is a being or creature who can detach their head, arms legs etc; from their torso.
Like many paranormal/supernatural creatures, they do have a predator/prey connection with ordinary people. They are so truly feared by people in the Philippines as they believe that the feed off fetus, placenta, young children, phlegm etc, with their long thin tongue, the tongue is inserted through one of the many entry's of the body (mouth, nose, ears, genitals.)
Their lifespan cannot be complete until they find someone to take their place. This is done when consuming phlegm, some kind of spawn (which i don't know much about) is placed inside the body, which phases them into a replacement aswang. until this operation is complete an aswang cannot completely die.
Overall, i love this creature, its dark, vampiric like and Incredibly morbid!