Security Iussue: /summon Witch ~ ~ ~ {Passengers:[{id:"Bat"},{id:"Chicken",Passengers:[{id:"Boat"}] }]} Looping minecraft Result: Killing Servers and Freezing Singleplayer worlds

You only have to use this command in Creative or Survival to spawn this mob Combination that freezes worlds (Blocl breaking and placing possible). Any Player will time out on a Server and singleplayer worlds will Crash the game if you try to save them.