Chicken Jockey

Chicken jockeys are the rare appearance of a baby zombie, baby zombified piglin, baby zombie villager, baby husk, or baby drowned riding a chicken.

Spawning
Each baby zombie, baby husk, baby zombie villager, baby zombified piglin, or baby drowned that spawns has a 5% chance to check for an existing chicken within a 10×6×10 box centered on the baby's spawn location and spawn riding one of those chickens if there are any. If it fails that 5% chance, there is an additional 5% chance of the baby zombie spawning mounted on a new chicken. In a chicken-free environment, each spawned zombie has a 0.25% chance of becoming a chicken jockey; if chickens are present, the chance increases to 0.4875%.

Chicken jockeys may spawn with items equipped. Baby zombified piglin versions of the chicken jockey always have a golden sword equipped, while baby drowned versions may have a trident. Although chickens take damage from magma blocks, baby zombified piglin jockeys still spawn on them, killing the chicken and leaving just the baby zombified piglin. Provoking the zombified piglin chicken jockey causes it to attack, like a normal zombified piglin.

Drops
The rider and the chicken each have separate drops when that part of the chicken jockey is killed.

Their drops are no different than if the zombie (or zombified piglin, zombie villager, husk, or drowned) and the chicken were standing alone.

Behavior

 * Chicken jockeys fall slowly and do not take fall damage, like normal chickens.
 * The chicken can run through 1 block high gaps. The baby zombie suffocates unless the above block is transparent.
 * The zombie in a chicken jockey can pick up/equip items.
 * The chicken (unless spawned with commands without the tag) does not lay eggs. However, they can still be bred into regular chickens.
 * Chicken jockeys despawn like zombies.
 * Chickens become passive again if the rider is killed, but still and may despawn and do not lay eggs.

Data values
Neither the chicken and rider's IDs nor the entity data are any different than if the chicken or rider were standing alone.

Trivia

 * $$, the chance for a baby zombie villager to spawn wearing full enchanted diamond armor holding an enchanted iron sword in its left hand while riding a chicken is about 1 in 2.91082&times;10-22, easily making it the rarest mob in the game.
 * Zombified piglin chicken jockeys can spawn from portals in the Overworld. Also, a normal chicken jockey may spawn in the Nether if a zombified piglin calls a normal zombie as reinforcement.
 * Name tags prevent the chickens from despawning, and they can be bred to spawn normal egg-laying, non-despawning chickens.
 * To prevent a chicken jockey from despawning, only the chicken needs to be name tagged, because riders of other entities never despawn.
 * The wither attempts to attack the chicken being ridden by the zombie and the zombie also takes damage.
 * A zombified piglin chicken jockey does not become hostile if the chicken is killed or attacked.
 * $$, if a zombie villager chicken jockey is cured, then the villager continues riding the chicken even after it grows up.