Minecraft wiki entry for Command_blocks_and_functions, associated text: Before the "SpawnPotentials" tag: The starter, which will never pop up again after the first time. If you want to see him again, you have to include him a second time under SpawnPotentials. Its appearance is just a random person in blue jeans (blue dyed leather leg armor), and a green dye shirt (green dyed leather tunic), with a wooden sword. He's a zombie under that mob head of it, of course.
Same thing, only this time, the wooden sword is 2 hits away from breaking.
The next one has a ninja-like appearance. This one is a skeleton under its mask, but he's been given an iron sword. All of its leather armor is dyed ninja-black. Skeletons with swords close the gap quicker than zombies, so watch out.
Zombie with a stone sword and chain armor, with Protection II on its mob head.
The next one has a gold sword, golden armor, a pumpkin on its head, and he's on fire! The pumpkin is enchanted with Protection II and Fire Resistance X in a desperate attempt to keep him on its feet and threatening the player for more than 5 seconds. It works, but if the player plays keep away then the zombie does tend to burn to death. Its sword has fire aspect too.
Iron Sword and Armor. Sharpness II on its sword, Protection II on its mob head.
The final mob, fake Herobrine, here has highly enchanted diamond armor (boots with Fire Protection IV and Feather Falling IV, leggings with Blast Protection IV, a chestplate with Protection IV, a mob head with Protection IV, Fire Protection IV, Blast Protection IV, Respiration III) and a diamond pickaxe enchanted with Sharpness IV, Smite IV, Bane of Arthropods IV, Looting III and Unbreaking III. Its also got the previously unseen CustomNameVisible (set to 1 for yes), a CustomName, and PersistenceRequired (set to 1 for yes). That last one will prevent it from ever despawning, although it can be killed normally. If you can get through that diamond armor and level 4 resistances.