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.

Spawning is not limited to the fortresses.

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.

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. Looting increases the chance by 1% per level (up to 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.

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

When the entity is attacked by a wither skeleton, they are inflicted with the wither effect for 10 seconds, which turns the health bar black and decreases the health by  every 2 seconds, similarly to poison. Wither skeletons deal on Easy,  on Normal and  on Hard.

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 will never pick up a bow under any circumstances; they do not use melee attack if they hold a bow in their main hand, instead they shoot fire arrows even if their bows are unenchanted.

Immunities
Like most Nether mobs, wither skeletons are immune to fire damage, and thus are not affected by fire blocks or lava. Wither skeletons are undead mobs, which means Wither bosses will not attack them, besides being unaffected by poison and regeneration effects. Their immunity to fire prevents them from burning in sunlight if transported through a nether portal or manually spawned in the Overworld, but they will still seek shade and water. Just like the skeletons they can not swim and end up sinking, but do not die drowned.

They are also immune to the damage done by a Wither Rose. However, if hit by a wither's skull, wither skeletons can be afflicted with the Wither effect.

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.
 * Wither skeletons run from wolves like normal skeletons do.