nobleblood - Because... well, Vlad comes from a long line of nobility, which would mean he literally has 'noble blood'. Yeah, lame, I know.
blackcatsrbad - Well, Cole is superstitious and a spaz, and one of the most popular superstitions out there is that black cats are bad luck. XD
noglass_slipper - Because Hannah's backstory is no fairy tale, and she doesn't quite believe in 'happily ever after'. Thus, there's no 'glass slipper' like the one which basically turned Cinderella into a princess.
lemortvivant - Taken right from POTO, actually, since it's mentioned that Erik was known as le mort vivant (the living dead) when he was with the Gypsies.