Mimic / Shapeshifter Mobs

A mob that mimics other mobs sounds. A mob that mimics other mobs body shape. A mob that acts and stays around another mob, but is not that mob. A mob that you can trade with if it mimics a villager or other intelligent mobs. A mob that changes depending on the biome it is in. A mob that can be hostile or passive depending on your actions to the mobs around it. A hidden guardian mob, like a golem but similar to normal mobs. A pet mob.