Dig down 10 blocks. At the bottom (Y level -10), place a row of hoppers pointing into double chests.
One block above the hoppers, place a layer of Campfires . Cover the campfires with Iron Trapdoors . The campfires provide light (so mobs despawn) and constant fire damage. lovely craft piston trap halloween update best
At ground level, place your 3x3 sticky pistons. On top of each piston, place a Slime Block (this prevents the mob from glitching out of the trap). On top of the slime block, place your decorative floor (Orange Wool/Carpet). Dig down 10 blocks
You build a circular arena (8x8). In the center, you place a vertical column of pistons that spin. On the outer ring, you place Soul Sand . The Halloween update made Soul Sand "slippery" for mobs. They walk onto it and slide toward the center. The rotating piston arm sweeps the arena every 4 seconds, pushing all mobs into a central pit of lava covered by a false piston floor. Cover the campfires with Iron Trapdoors