Easy it's just a Ghast Riding a GIANT
Note: Minify the command to avoid issues :)
The Creepiest Giant EVER
Hider Killer
Annoying Villager Murderer
Notch Book Troll
Pet ENDER DRAGON!!!!!
Wither Storm Boss in ONE COMMAND
HEROBRINE COMMAND
HEROBRINE BOSS BATTLE (See YouTube for details)