The server has a nice plugin which prefend that mobs like Withers and Creepers can destroy blocks (unless you give them permission in your own claim to do so)
A thing that is normally impossible, holding a Wither as pet into a cage of glass is now an option. In november I made a descision to tear down my main building (actually, basement : storage and smelting room + plus little zoo) I dug out a big hole with the bottom at y46 to start over fresh. Well, i caught a nitwit baby zombie just for fun, which started my little collection of some special mobs.
Inventory:
Witch
Enderman + Endermite
Zombie Villager with armor
Zombie nitwit baby
3 Silverfish
Spider
Creeper
Magmacube
And intergrated as roof for my storage room, an aquarium with 16 guardians (brought over 2000 blocks)!
At 2nd floor of the underground:
3 polar bears + 2 wolves, The large aquarium with 16 guardians and my favourite: The Wither with his buddy the Nitwit
Like to see? Ask me and come visit my personal zoo of freaks.