Very Hard. Try it out.
Note: Minify the command to avoid issues :)
Ride a Ender Dragon!
Mystery Mob Boss Fight!
Smash Brothers Home Run Bat!
Emerald Armor!!!!! Check It Out!
Pet ENDER DRAGON!!!!!
Wither Storm Boss in ONE COMMAND
HEROBRINE COMMAND
HEROBRINE BOSS BATTLE (See YouTube for details)