Bukkit

Hey, Here a new mob you could add that I've been thinking of:

Vampire:
Where's a black leather vest
Is Invisible
Wears a WitherSkull head
Holds a Ghast Tear for a fang
Poisons you when your hit for a bleeding effect
Moves 1.5x faster than you

You're missing a really important feature of vampires from RPGs.

Here's a hint: what do they gain from attacking people?

There's so much more you could have done with this idea, but you only put this much forth. Allow me to nuance it much more.

I don't see why vampires should be invisible. There's nothing associated with vampires that makes them invisible. Nor did they hold fangs in their hands and attack people with it. I would think that they'd be unarmed.

One really interesting feature would be to give them a vulnerability to the arrow item, as those come closest to "stakes", along with golden weapons/tools which are otherwise useless.