Wither Skeleton

Wither skeletons are variants of skeletons found in fortresses and The Nether. They spawn with stone swords.

Spawning
Wither skeletons spawn in fortresses at a light level of 7 or less, in groups of 1-5.

Spiders and cave spiders spawned in the Nether (via spawn egg, monster spawner, etc.), have a 0.8% chance of spawning as a Wither Jockey.

Wither
On normal difficulty or harder, the wither will spawn 4 wither skeletons when below half health.

Spawn eggs
A wither skeleton spawn egg can be found in the Creative inventory. This egg spawns only wither skeletons.

Drops
When killed, wither skeletons will drop 0–2 s.

Wither skeletons have a $1/3$ chance to drop a single. The maximum amount of coal is increased by 1 per level of Looting. The chance of a wither skeleton not dropping any coal can be found using the formula. For example, Looting III gives a $1/3$ chance of not dropping any coal. All other amounts have an equal chance of occurring.

They also have a 2.5% chance to drop 1 when killed by the player or tamed wolf. Looting increases the chance by 1% per level (5.5% chance of a drop with Looting III). They will always drop their skull if killed by a charged creeper.

They have an 8.5% chance of dropping their stone sword, which will have a random durability, and always be un-enchanted.

They drop 5 experience when killed by a player or tamed wolf.

Halloween
If a wither skeleton wearing a pumpkin or jack o'lantern is killed using a tool enchanted with Looting, there will be a chance equivalent to the level of Looting used to drop the pumpkin or jack o'lantern, up to a maximum of a 3% chance of a drop.

On Halloween, wither skeletons have a 22.5% chance of spawning wearing a pumpkin and a 2.5% chance of spawning wearing a jack o'lantern.

Behavior
Wither skeletons wander when idle, but will sprint at the player's walking speed when attacking players, snow golems, baby turtles and iron golems within 16 blocks.

When an entity is attacked, it is inflicted with the wither effect for 10 seconds in any difficulty, which turns the health bar black and decreases the health by  every 2 seconds, similarly to poison.

Like other undead mobs, wither skeletons may spawn with the ability to pick up dropped melee weapons and armor. Although they may spawn with the ability to pick up items, wither skeletons never pick up a bow under any circumstances; if they hold a bow in their main hand, they shoot flaming arrows even if their bows are unenchanted.

Mob type
Wither skeletons are immune to poison and fire, this prevents them from burning in sunlight, but they still seek shade and water. Just like the skeletons they can not swim and end up sinking but do not take drowning damage.

Being undead, a Wither will not attack them.

If hit by a wither's skull, a wither skeleton is afflicted with the Wither effect.

Finally, a wither skeleton is immune to the damage done by a Wither Rose.

Data values
Wither skeletons have entity data associated with them that contain various properties of the mob.

Trivia

 * If a wither skeleton is wielding a bow (which can be spawned with ), it will use it like an ordinary skeleton, but the arrows it shoots will always be set on fire, regardless of enchantments.
 * Like other skeleton variants, wither skeletons do not know how to use a crossbow, despite the same using method as a bow.
 * Wither skeletons run from wolves like normal skeletons do.