This actually needs two command blocks.
Note: Minify the command to avoid issues :)
sp00ky sign
UNICORN HORN!!! ONE EASY COMMAND!!!
ME WANT DIAMONDS
TroSup (Troll Supplies)
Pet ENDER DRAGON!!!!!
Wither Storm Boss in ONE COMMAND
HEROBRINE COMMAND
HEROBRINE BOSS BATTLE (See YouTube for details)