There were no new mobs added in Minecraft 1.4.
There are no mobs in this group.
A new boss was added, the Wither. Wither skeletons were added to the nether with the skull loot drop that could be used to summon the Wither Boox. Witches and zombie villagers explained the villager face design further into the world. Zombie villagers provided a method that players could repopulate the world with cured villagers.