Three Wither Skeletons

Wither Skeleton: Taller and charred dark-gray or black, found in Nether Fortresses, and wields a stone sword instead of a bow.

The Wither Skeleton is taller than the regular skeleton and is slightly shorter than the Enderman, making it the third tallest hostile mob in the game. It almost looks charred, possibly because of fire and lava, or because of the wither effect's color. It holds a stone sword instead of a bow.

Upon death, a Wither Skeleton will drop Coal, Bones, a Stone Sword, and rarely (1 in 50 chance) their Head. Three Wither Skeleton Heads and four Soul Sand blocks are required in order to spawn The Wither.

Wither Skeletons will only spawn within Nether Fortresses as of the 1.4 pre-release. It is assumed that they follow the same rules for spawning as blazes, which will only spawn naturally, and not from a spawn where the pack spawn is selected within a nether fortress. From this pack spawn, the mobs can be spawned in close to or even inside the fortress.

Unlike regular Skeletons, wither skeletons carry swords instead of bows. In appearance, they are black and slightly taller than the usual skeletons. If a player is hit by a wither skeleton, a player will be infected with the wither effect, which will slowly drain their health. Unlike poison, however, it can kill a player. Using a Skeleton Spawn egg in Creative Mode in the Nether has a 75% chance of forming a Wither Skeleton instead of a regular skeleton.