Let's discuss this highly-neglected monster girl.
Does anyone think of the main difference between a manananggal and a dullahan being that the upper body and lower body not being able to feel what the other is doing while separated? That way, if you get housed by one during an exchange program, while the sexually oblivious upper half is out doing errands during the day, the spicy lower half keeps you company and maintains a secret relationship with you, the upper half none the wiser that her lower half is consistently doing all manner of lewd things with you each and every day.
The only real major downside I can think of when it comes to her is that, since she's from the Phillipines, if she gets too absorbed in human culture, she will bully you a bit too hard if you're not circumcised. But then again, that's like expecting other monster girls to care that much about the sexual preferences of others.