Jockey

A Jockey is a rare mob in which a Hostile Mobs spawns riding another Mob. They were first added in Update 0.11.0.

Spider Jockey
A Spider Jockey spawns as a Skeleton riding a Spider or a Cave Spider. It is a very dangerous mob as the Skeleton uses ranged and the Spider uses melee, making it a deadly combination. In Update 0.14.0, a Baby Zombie can also ride a Spider.

Chicken Jockey
A Chicken Jockey spawns as a Baby Zombie or Baby Zombie Pigman riding a Chicken. It moves very fast, making it very hard to outrun. Only the Zombie is hostile, not the Chicken.

Wolf Jockey
A Wolf Jockey spawns as a Baby Zombie riding a Hostile Wolf. It was added in Update 0.14.0.

Cow Jockey
A Cow Jockey spawns as a  Baby Zombie  riding a Cow. It was added in  Update 0.14.0.

Zombie Jockey
A Zombie Jockey spawns as a Baby Zombie riding a Zombie. It was added in the mcpe Update 0.14.0. A zombie jockey is a also very dangerous

Pig Jockey
A Pig jockey spawns as a Baby Zombie riding a Pig. It was added in Update 0.14.0.

Ocelot Jockey
An Ocelot Jockey spawns as a Baby Zombie riding an Ocelot. It was added in Update 0.14.0.

Sheep Jockey
A Sheep Jockey spawns as a Baby Zombie riding a Sheep. It was added in the Minecraft Update 0.14.0.

Trivia

 * Spider/zombie Jockeys, Cave Spider Jockeys, Cow Jockey, Zombie Jockey, Pig Jockey, Ocelot Jockey, Sheep Jockey and Wolf Jockeys are exclusive to Minecraft Pocket Edition.
 * Wither Skeletons also have a very small chance to spawn riding a Spider or a Cave Spider creating a Wither Jockey.