[Snapshot]BOSS Spawner

/setblock ~0 ~1 ~0 minecraft:mob_spawner 0 replace {SpawnCount:1,SpawnRange:1,Delay:0,MaxSpawnDelay:100,MinSpawnDelay:100,MaxNearbyEntities:16,RequiredPlayerRange:2,EntityId:Chicken,SpawnData:{Pos:[-255.5d,8.0d,136.5d],Riding:{id:FallingSand,Block:minecraft:redstone_block,Data:0,Time:1,DropItem:1,Riding:{id:FallingSand,Block:minecraft:command_block,Data:0,Time:1,DropItem:1,TileEntityData:{Command:"/fill ~ ~1 ~ ~ ~-1 ~ minecraft:air"}}}}}

/setblock ~0 ~1 ~0 minecraft:mob_spawner 0 replace {
	SpawnCount:1,
	SpawnRange:1,
	Delay:0,
	MaxSpawnDelay:100,
	MinSpawnDelay:100,
	MaxNearbyEntities:16,
	RequiredPlayerRange:2,
	EntityId:Chicken,
	SpawnData:{
		Pos:[
			-255.5d,
			8.0d,
			136.5d
		],
		Riding:{
			id:FallingSand,
			Block:minecraft:redstone_block,
			Data:0,
			Time:1,
			DropItem:1,
			Riding:{
				id:FallingSand,
				Block:minecraft:command_block,
				Data:0,
				Time:1,
				DropItem:1,
				TileEntityData:{
					Command:"/fill ~ ~1 ~ ~ ~-1 ~ minecraft:air"
				}
			}
		}
	}
}