Undeads are feared as opponents due to the many various forms of
attack they can throw at their targets. One such attack, is to attempt to
drain the life energy from their victim. Many undead thrive on this
ability, taking their victims life energy, and claiming it as their own.
Those who follow the dark gods also can learn this power and use it to
increase their own power. Many dark wizards have gained all their power
from sucking out the life of their fallen foes.