If any of you want to have a simple way to harvest mobs. If you make it in the ground you cut a 3x3 box in the ground, then make canals 8 long on each of the sides. TIP: put water on the sides of the canal filling in the middle allowing you to refill your buckets. Then make a ledge above the blocks on the outside of the canals. Then make 8x8 platforms for mobs to spawn on. Then make a wall two higher than the spawning platforms and make a ceiling. then start strip mining in your 3x3 hole. Then make the hole 25 layers down and wait at the bottom for monsters to spawn and fall into the water, they will then be pushed into the hole fall and be killed. You will also want to make a ledge to hide under while monsters fall so they can not attack you while falling. For better results you can build these spawners on top of each other. I will hopefully make another post or edit this one and add photos. Simple and kills all mobs but is not efficient unless more than two are built. I have some photos but I cant put them on my extra facebook unless someone adds me. So please add me with some junk facebook account so I can show them to you all. Add Bobby Burlap
Simple mob killer