Wither Skeletons are related to Skeletons, except they have black skulls and dont have a nose peace. They sometimes but Rarely, would hold Stone or Golden Swords. They do not hold bows/ nor arrows. unlike the Wither Boss, their eyes are black.
Wither Skeletons are hostile. They would instantly attack you when it catches eye sight with you. Wither Skeletons would run towards you like zombies or Zombie Pigmen.
Wither Skeletons will spawn on Nether Fortresses.
Wither Skeletons will drop Coal, for no apparent reason. maybe because they are dark black. Also they would drop Bones because they are Skeletons. And rarely they would drop Wither Skeleton Heads, which are the Ingredients for making Wither.