The Undead are a species of Others that are born from the dead and dying. Formed through either grudges or disturbing the balance between life and death, these Others are often once Humans or Practitioners.
The art of using undeads is called Necromancy.
Undeads don't change much from their original appearances while alive, besides whatever toll is taken on their body. So far there have been:
Any usefulness that stems from an undead is the natural abilities they had in life or as basic muscle.