Hack Slash/WMG

Cassie Hack is a Slasher.
Think about it: Cassie says that the only thing she knows for certain about Slashers is that "they're mean and hard to kill....I'm Cassie Hack. I'm mean, I'm hard to kill, and I hunt slashers." So Slashers are, in effect, serial killers who are especially mean and difficult to kill. What is Cassie but a serial killer (of serial killers) who is mean and hard to kill? Clearly, Cassie was murdered, probably by her own mother, but Cassie was so driven that she rose from the dead to seek revenge on Slashers like her mother. Because of the trauma, however, she suppressed the memory of her own death; also, she clearly wasn't disfigured by her death.
 * Supported by the fact that, assuming that the Black Lamp Society is correct, there is a hereditary component to being a Slasher. It's been confirmed repeatedly that there is definitely a biological component to being one.
 * Also Samhain, who was not merely more moral than most slashers but more stereotypically attractive. Although Cassie hasn't shown anything you could really call super-healing yet.
 * No obvious super-healing, but her survivability is extraordinary.

Bomb Queen is Cassie's Alternate Universe Evil Counterpart
They look kind of similar; Cassie could've become like BQ, a psychotically depraved hedonistic thrill killer and the champion of psychos, if she had chosen a different path, or if she just completely snaps one day. Could possibly tie into the above.
 * Hack/Slash doesn't suck though.
 * Another tie-in to the opposites theory! :D

Vlad isn't entirely human
It's been revealed that some demons/extra-dimensional things use humans for breeding, so it doesn't seem a big leap to actual hybridisation. Hence his looks, strength, and Parental Abandonment. His lung problems are probably because his lungs aren't completely optimised to Earth atmosphere: since acidic urban air pollution makes them worse I suspect that one of his parent's home environment had a more alkaline nature than Earth, maybe an ammonia-heavy atmosphere.
 * Jossed by Me Without You. It features his perfectly normal mother and father, and shows his maternal grandfather (an apparent descendent of Sawney Beane) has whatever disorder Vlad does, though apparently much more severe due to either age or because he didn't bother to work through it like Vlad did.

Vlad is either an Alternate Universe Good Counterpart to Jason Vorhees, or Jason's relative.
Both are giants with deformed faces and skulls that walk around and killing stuff with knives. Both are also not the sharpest knives in the drawer. Maybe Vlad is what Jason Vorhees or someone with his genes would have grown into with marginally better parenting and not so much bullying.
 * I think Seeley once said he envisioned Vlad as a good version of Jason.

Cassie will get romantically involved with Cat Curio.
Cassie has said she won't let herself get attached to anyone who can't handle the kind of life she and Vlad lead. Cat is already in the process of becoming precisely that sort of person; Curio already wants to hunt slashers and fight the Black Lamp society. They'll eventually become a Battle Couple.
 * It would certainly explain this incentive cover.