Minecraft wiki entry for Spawner_traps, associated text: This type only applies to zombie and skeleton mob spawners. Sunlight-based traps are made by placing water below a spawner. This water will flow from one side to another. Where the water stops, dig a pit a few levels down. This will drop the mobs into the pit. To finish, make sure that the pit is open to sunlight. This sunlight will burn the mobs alive. An example of this can be found here: https://youtu.be/1AijahlBqyU .