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.

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. The maximum drop is increased by 1 per level of Looting, for a maximum of 0-5 bones with Looting III.
 * $1/3$ chance to drop a single . Each level of Looting increases the maximum drop by 1, so that Looting I drops 0-2 coal with an average of 0.67 coal per kill, Looting II drops 0-3 coal with an average of 1.11 coal per kill, and Looting III drops 0-4 coal with an average of 1.58 coal per kill.
 * 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, for a maximum of 5.5% chance with Looting III. 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. This chance increases by 1% per level of Looting, for a maximum of 11.5% chance with Looting III.
 * They drop when killed by a player or tamed wolf. If it has armor, an additional 1 to 3 experience is dropped per piece.

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.