Seconded.

Argh, the auto-formatting on the comments really wrecks that last post. I put together a more readable version and threw it up on my own site: http://dagda-mor.blogspot.com/2011/05/re-which-bite-wins.html

It all depends on precisely which variety of each monster is being used.

Let’s start by saying each has a contrived biological explanation:
-Zombies are an actual virus, spread via bodily fluids. One explanation I always liked, from a few incarnations of Resident Evil, was that it was a combination of a destructive ebola strain (which would kill people too fast to actually spread) and a failed viral vector which stimulated cell growth & activity (in hopes of creating supersoldiers, instead of bodybuilders with lots and lots of cancer).
-Vampirism is a disease, bloodborne microorganisms (think malaria) that alter your bodily chemistry to make you sociopathic, alert, unnaturally strong, oversensitive to light, in need of blood, etc.
-Werewolves. . .hmm. Let’s say that werewolves are a hereditary genetic thing- because genetic traits aren’t always just recessive or dominant. There are disorders that run in a family but have little clear pattern, because the potential is there in the genes but other factors are needed to push you over the brink. Like your diet, or high levels of stress. From being bitten by a werewolf. Uh, and it has to be a werewolf because there’s also a biochemical factor that’s induced by a werewolf’s saliva. (Werewolf french kisses will thus also induce a transformation, but they almost never do that to someone)

If we assume each of these transformations’ initial effect happens over the effect of 5 minutes, what happens when they’re combined? Here’s where I really start throwing out bullcrap (instead of rigorously looking up concepts like “viral vectors” on wikipedia, for like 5 whole minutes, and *then* using them in my bullcrap).

The zombie virus is spreading throughout your bloodstream, altering the behavior of your body’s cells so that they work 80-hour weeks with little oversight or direction. The effects would not be obvious right away- the subject would be feverish and delirious, with the viral vectors needing longer periods of time to reach the central nervous system.

The werewolf stimuli simultaneously triggers a change in the subject’s. . .uh. . .he grows hair and stuff, ok? Look, this just getting ridicu

Ahem. The werewolf stimuli simultaneously triggers its own change in the subject’s biological functions, activating the latent potential behaviors of his organs. His body starts to reconfigure itself, with the viral zombie interference hindering the development in some cases and amplifying it in others.

The increase in pulse rate and vital activities would give the bloodborne vampire microorganisms a boost, letting them take effect quickly and with more potency. So while the subject begins having difficulty distinguishing reality from his imagination (the zombie virus’ initial delirium), and having all kinds of predatory carnivore impulses, he’s also becoming more alert, obsessive-compulsive, and sociopathically cunning.

Soon the delirium will fade as the zombie virus reaches the brain, and the higher thought processes turn to empty static. But where a normal brain would thus be left in a constant state of dazed distraction and simple agitation, this brain has different kinds of things going on under the hood. Predatory impulses to hunt and prowl, to lurk and carefully monitor the surroundings, to lunge forward and attack your prey with terrible ferocity.

Physically, the subject’s skin becomes pale and lifeless before it can grow much hair, and his terrified babbling quickly gives way to guttural groans and animal growls. The scientists high five one another as the subject flexes ineffectively against the restraints, concluding that they have basically produced a zombie with sharp teeth that snarls alot.

They aren’t realizing not realizing the changes that have only just begun in the subject’s muscles. That they’ve started growing to fulfill their latent potential, AND have been told by viral vectors to work overtime, AND are being treated to a special biochemical cocktail courtesy of bloodborne symbiotic microorganisms. Meaning that in a few days the subject will become twice as strong. . .three times over. (That’s right- EXPONENTIALLY stronger)

And because there’s nothing else left for a zombie to feel, because it fuels everything the wolf has evolved to accomplish, because it compels the vampire as a terrible addiction: the subject will be driven by an unimaginably strong hunger.

Howzat?

I’m leaning towards primarily zombie-ish traits at the moment. Vampires are a demonic infestation, destroying the soul, but leaving the mind intact. Still, it takes time.

Meanwhile, zombiedom is a purely physical infection, and typically a little faster. It rots brain tissue, which would leave the host body less intelligent on revival. Probably demonic, but incapable of reason without a working host brain to act through. Simple.

As for the werewolf, it’s a curse. Probably hits the body at full moon no matter the body’s state.

So, we’ve got a nigh indestructable semi-demonic monster that gets even nastier come full moon, but isn’t much for planning. Would probably tear its victims to shreds, though, so getting more wouldn’t be an issue.

As for killing, I suspect a blessed silver bullet to the skull would work. And running water, invitation, all those defenses still apply.

On the other hand, if Subject A is the new Adam, he should be fine. Just a little banged up from chewing. Artificially mockeries of life tend to resist curses.