Also works with magma cubes -
/summon LavaSlime ~ ~ ~ {Size:20}
Note: Minify the command to avoid issues :)
Difficulty IMPOSSIBLE!!!
VERY FAST BOOTS!!!!!!
small groWING WITHER!!!!!
SUPER ARMOR!!!!!!!!!!!!! #1:boots
Pet ENDER DRAGON!!!!!
Wither Storm Boss in ONE COMMAND
HEROBRINE COMMAND
HEROBRINE BOSS BATTLE (See YouTube for details)