/summon FallingSand ~ ~2 ~ {Block:barrier,CustomName:上,Time:1,DropItem:0,CustomNameVisible:1,Riding:{id:FallingSand,Block:barrier,CustomName:中,CustomNameVisible:1,Time:1,DropItem:0,Riding:{id:FallingSand,Block:barrier,CustomName:下,CustomNameVisible:1,Time:1,DropItem:0,Riding:{id:WitherSkull,direction:[0.0,0.0,0.0]}}}}