Minecraft wiki entry for Spawner_traps, associated text: For this trap, you need to dig a large pit 22 blocks deep under the dungeon, or make a water elevator taking them upwards so you can stay near the monster spawner. Go to the bottom of the pit and place water in a fashion so that it should flow towards a wall. Then make a room where the water is flowing. This is where you will stay while finishing off the mobs. Make the room so that it has a one-block hole where you can see the mob drop zone. Hopefully, mobs should spawn, fall down the pit and survive with half a heart, get pushed towards you by the water current, and get killed by a single hit. If you like, you can bring food along as your hunger will deplete over time. This should provide normal as well as rare mob drops and experience levels, making it quite useful. Another technique is to leave your player by the dungeon for a couple of hours, overnight is suggested, and there will be at least a hundred monsters waiting to be harvested. Keep in mind that the maxEntityCramming gamerule can limit the output.