A lot of old representations of vampires eschew the whole bat thing in favour of a more bird-themed approach - female vampires in particular seem to be often shown as harpy-like things: weird, scaly sphinx-birds that torture and kill men. I might post some of these paintings when I can be bothered.
Concentrating more on the bird-pet-thing now - the idea is that this vampire rides around on this huge, strange bird monster that who eerily resembles him - kind of a cross between the witch's bird familiar from Spirited Away and the Helmaroc King from Legend of Zelda: Wind Waker.
I'm conscious the whole idea of the face being a false mask concealing a gigantic mouth is totally ripped off from that No-Face demon in Spirited Away, too. Plus, I'm not sure how the CG guys would rig that. I imagine the feathers looking like Howl's bird form from Howl's Moving Castle, too. So much Miyazaki reference ;_; I'm not like a massive Miyazaki fan ok
Plus I think the rider still needs to be jazzed up somehow.