This tutorial teaches you how to build my practical hostile mob system.Pros: Compact, Easy, Quick, & Cheap to build. Doesn't cause block updates that would cause lag to your game. Works well in SMP.Cons: Lower efficiency. Mobs are not forced off spawning pads so they may get stuck.Mobs will not spawn within 24 blocks of your player.Mobs will despawn if over 32 blocks from your player.Mobs will go into sleep mode if over 32 blocks from your player.Mobs will almost instantly despawn if over 128 blocks from your player.Mobs can spawn in any loaded chunk in light levels 7 or less. Mobs are more likely to spawn in dark areas as they approach light level 0.