Vampire

These nocturnal creatures suck the blood of their enemies for life.  They
have innate abilities at sneaking around the world without being detected. 
Their supernatural eye-sight allows them to see perfectly in complete
darkness.  Although vampires are immune to any form of disease, they are
quite vulnerable to sunlight and holy light.  Also, they receive no
nourishment from food and drink.  Drinking blood from other living creatures
is the only way a vampire can curb hunger and thirst.  The sneaky,
backstabbing, blood-sucking fiends make excellent thieves and warriors.