Minecraft wiki entry for Mob_farm, associated text: EXP farms are systems that capture and soften up the mobs, but rely on the player to deliver the killing blow, so that the rare drops and experience can be gathered. An example would be a nearly-lethal falling height which would reduce the majority of mobs to half a heart, easily killed even without a weapon. However, such systems are only as good as the player using them, and in constant danger of being destroyed by creepers if not built out of obsidian, or if the player is out of sight of the creeper, in which case it does not explode. Also on bedrock edition one can make a piston push a trident back and forth for AFK xp.