Hostile Mobs are entities that pursue and attack the Player if they are within visible range. Hostile mobs have different modes of attacking the Player.
Jockeys were added in Update 0.11.0 and could be found as rare spawns out of normal Spider and Zombie spawns.
More Jockeys involving Baby Zombies riding a Passive Mob or a Zombie, which were version exclusives, were added in Update 0.14.0.
Ocelots are coded as Hostile Mobs but are actually Passive Mobs.
As of Update 1.0, Endermites are the smallest Hostile Mobs.
Tiny Slimes are hostile to the Player but don't deal damage.
In the PC version there is a hostile variant of the Rabbit called The Killer Bunny, although it is unknown whether it will be added to Minecraft PE in the future or not.
Before Update 0.16.0, Hostile Mobs wielding Items had no chance of dropping the wielded item when killed.
If The Player positions himself/herself within Double Tall Grass, Hostile Mobs will not be able to detect them.