Minecraft wiki entry for Wither_Skeleton, associated text: A wither skeleton in the Overworld.
A wither jockey.
A wither skeleton next to the wall of a nether fortress.
A preview of two wither skeletons in the soul sand valley.
A wither skeleton with a carved pumpkin on its head.
A wither skeleton and a blaze idling in a Nether fortress.
A wither skeleton and two blazes near a blaze spawner.
Wither skeleton wearing a pumpkin on Halloween.