It is a Zombie riding a Wither Skeleton Skull.
Have Fun!
Note: Minify the command to avoid issues :)
Villager Calvary Soldier
Red Order Form
Spell Tome of Heath II
Potion of Defense (Resistance)
Pet ENDER DRAGON!!!!!
Wither Storm Boss in ONE COMMAND
HEROBRINE COMMAND
HEROBRINE BOSS BATTLE (See YouTube for details)