Chicken Jockey

Chicken Jockeys are an extremely rare mob. They consist of a Baby Zombie, Baby Zombie Villager, or Baby Zombie Pigman riding a Chicken.

Behavior
Chicken Jockeys run around like Baby Zombies, instead of using the chicken AI.
 * Even though the Zombie AI is used, the chicken still randomly lays eggs.
 * Chicken Jockeys will not avoid bumping into walls that would potentially suffocate the Baby Zombie.
 * Chicken Jockeys do not take fall damage, as the chicken flaps its wings quickly, slowing the falling speed.
 * The chicken moves at the speed of the Baby Zombie, which is much faster than a normal chicken.
 * Chicken Jockeys can track the player over a very large distance.
 * Like Zombies, the Chicken Jockey will also track villagers.
 * Although a Chicken Jockey's hitbox is 3 blocks tall, the chicken can still run through 1 block high gaps. If the above block is solid, the Baby Zombie will take suffocation damage.
 * Chicken Jockeys can pick up/equip ground items.

Spawn
Each baby zombie or baby Zombie Pigman that spawns has a 5% chance to spawn riding a chicken. This includes baby villagers turning into baby zombie villagers. There is an additional 5% chance of it mounting any existing chicken within a 10x6x10 box centered on the baby zombie's spawn location. In a chicken-free environment, this gives each spawned zombie 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 Zombie Pigmen versions of the Chicken Jockey will always have their Golden Sword equipped.

Trivia

 * The command to spawn a Chicken Jockey is
 * This is not exactly the same mob, but it is close, the real Chicken Jockey is positioned lower on the Chicken's back, which you can get by spawning a large number of zombies, do this in daylight so adults burn. Then kill the babies that don't have a chicken to ride.
 * The baby zombie's hitbox is larger than the chicken's.
 * Attacking the chicken may harm the zombie instead, unless the player carefully attacks its feet.
 * If the chicken moves too close to a wall two blocks high, the zombie half will take suffocation damage unless the upper block is transparent.
 * Since they can spawn in the Nether, eggs, feathers, and raw chicken are now renewable in that dimension, without having to bring eggs from the Overworld.
 * When a Splash Potion of Harming is tossed at a Chicken Jockey, the Chicken dies, but the Baby Zombie gains some health. Vice versa, if a Splash Potion of Instant Health is thrown at a Chicken Jockey, the Chicken is healed, but the Baby Zombie takes damage (and may be killed). This makes healing them as a single mob very unlikely.
 * Chicken Jockeys and Spider Jockeys are the only mobs that cannot pass through portals.
 * It is possible to have a pigman chicken jockey in the Overworld by having a portal with a chicken near it.
 * It is also possible to have a generic chicken jockey in the Nether by killing a zombie pigman, spawning in normal zombies.
 * If the zombie happens to be a villager zombie, curing it will separate the formed villager from the chicken.