Manananggal comes from the root word "tanggal" (remove/disjoin), and taken literally, it means "one who removes." Essentially, the creature is a witch that has a specific power at night - it disjoins from the lower half of its body, changes its upper limbs into wings, and flies off into the night in search of innards to consume. In this form, it feeds via its elongated tongue that it uses like a straw. Once it finds a suitable prey, it injects its tongue through the belly and feeds.
Most stories about the manananggal ended with someone (be it the child or spouse of a former victim, or a trio of crafty teenage boys) finding the manananggal's lower half and destroying this this immobile half. Without the lower half as a sort of compass, it cannot find its way back before dawn, and the light of the sun will destroy it eventually. That makes for a good story, for sure, but we felt that more should be done with the lower half for 4E. So we made a decision to make the lower half more than just an immobile phylactery of sorts.
Thus, when the asuang disjoins (an event that can happen in combat), the lower half fights on. The destruction of a lower half endangers the manananggal, however, so it is usually inits best interest to keep the lower half hidden while the upper half wades on fearlessly. Guess what the combat role of the lower half will be. :P
Because of its hunger for flesh as well as its vulnerability to sunlight, the manananggal is usually referred to as a vampire. Our upcoming ebook explores this connection, but vampires in D&D are undead, and all things considered, the manananngal do not qualify as such. Instead, we looked at the origins of the monster, and derived its creature type from there.
It is said that the source of power for the manananggals reside in a black chick hiding in their bodies. These demonlings can be forced out by tying the asuang upside-down and turning the creature over and over. Eventually the creature will vommit, and the demonling can be caught and killed.
Unlike other asuangs who have inherited their condition, manananggals are not born. Instead, manananggal families keep tiktiks, as we decided to call these black demon chicks. Each tiktik is the blessing of a mighty demon lord or one of its vassals onto the family. Most frequently it is a demon lord of elemental air (Pazazu, Puzaza? Puzuza?). In addition to the statistics for the manananggal, there will be stats for the tiktik in Asuang: Shapeshifting Horrors.