Ok - the other day Spikedemon223 and I tried out this new command. It's a randomly generating stone structure. We've made a view, you can catch it on YouTube. Here is the full command.​ summon falling_block ~ ~1 ~ {Block:stone,Time:1,Passengers:[{id:falling_block,Block:redstone_block,Time:1,Passengers:[{id:falling_block,Block:activator_rail,Time:1,Passengers:[{id:commandblock_minecart,Command:"gamerule commandBlockOutput false"},{id:commandblock_minecart,Command:"fill ~2 ~-3