Wither Skeleton

Wither skeletons are hostile mobs with stone swords found in fortresses.

Spawning
Wither skeletons spawn in fortresses at a light level of 7 or less, in groups of 5. They only spawn on top of Nether Bricks.

Spiders and cave spiders spawned in the Nether have a 0.8% chance of spawning as a wither jockey.

On normal or hard difficulties, the wither spawns 4 wither skeletons when below half health.
 * Wither

Drops

 * 0 to 2 s.
 * $1/3$ chance to drop a single . With 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.
 * 2.5% chance to drop 1 wither skeleton skull when killed by the player or tamed wolf. Looting increases the chance by 1% per level. Their skull is always dropped if killed by a charged creeper.
 * 8.5% chance of dropping their stone sword, which has a random durability and is unenchanted.
 * They drop when killed by a player or tamed wolf. If it has armor, an additional 1 to 3 experience is dropped.

Halloween in Java Edition
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.

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

Behavior
Wither skeletons wander when idle, but sprint to attack players, snow golems, iron golems, baby turtles and piglins 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 it by  every 2 seconds, similarly to poison. A wither doesn't attack them.

Depending of regional difficulty, up to 55% of wither skeletons pick up dropped iron, diamond or netherite swords and armor in normal or hard. Although they may, wither skeletons never take bows; if they hold a bow (which can be with ) they shoot flaming arrows even if their bows are unenchanted.

Wither skeletons are immune to regeneration, poison, fire and the wither effect. They still seek for shade and water whereas under sunlight; they sink in water, don't swim and they don't drown. They sprint away from wolves and cannot use crossbows.

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