Fallen Mobs/Animals

Fallen mobs are super rare versions of common mobs (Creepers, zombies, skeletons, spiders) that are much more powerful. Fallen mobs are super rare, possibly 1 Fallen Mob for every normal mob. They have twice the health, deal twice the damage, are faster, and have a further range. (Can detect and chase after players from a further distance)

The Fallen state can also be true for animals too!

Fallen Animals are naturally aggressive. They won't do as much damage as Fallen Mobs, but are still quite terrifying. The fallen chicken could be just as fast (if not faster) than baby zombies. 

Fallen Mobs are very likely to drop expensive loot (diamonds, possibly diamond armor, normal armor, basically anything that wouldn't normally drop from a chicken or zombie)