Note: Minify the command to avoid issues :)
Evil Golems in 1 command
BlazedWither boss (Literally unkillable) Read the comments
Herobrine Spawner! (1.8,Spawns only at the night) A VERY POWERFUL HEROBRINE
HOTEL ONLY ONE COMMAND BLOCK
"Herobrine joined the game."
BIG TNT BLOCK!