Mob spawning mechanics: Part one Spawners: Part two Guide to building mob traps: Part three I'm going to be putting this in chunks to save it. When all of the information is stated, I will put everything that you need to know in Green. Could a moderator sticky this so people will know how to get this information? Part one: Mob spawning mechanics Hostile mobs have a spawning cycle once every game tick (1/20th of a second), while passive mobs can only spawn once every 400 ticks. Because of this skeletons, zombies, spiders, etc, can spawn at any time. Mobs can spawn in a 240x240 block around the player. But when there are multiple players, mobs can spawn within this distance of any of them(therefore, all over your island). However, if you move 128 blocks away from a mob it will despawn, so the mob spawning area is completely limited to a sphere with a radius of 128 blocks, centered at each player. Because of this you need to have the trap within 110 blocks of you or so. But it needs to be within 240 blocks of you. This is fairly easy to achieve as long as you don't leave your island right? No. The number of mobs able to spawn is directionally proportianate to the number of chunks where they can spawn. To calculate the cap, the spawning area is expanded by one chunk in every direction, so that it is 17x17 chunks in size, and then the total number of chunks is plugged into the following formula: Constant * chunks / 256 = Maximum cap Hostile = 70 Passive = 15 Water = 5 Therefore if you have one mob spawner and the rest of your island is lit up, then I figured it would be about 6 chunks where they could actually spawn. 70 * 6 / 256 = 16.15 This means that the mob cap on your island would be about 16. Now, I have a massive castle, and I made everything completely dark, and there were about 15-20 mobs on each floor. My whole island is approx 12 chunks or so, so... 70 * 13 /256 = 32.30 This doesn't add up does it? Well in multiplayer, chunks that are in range of multiple players are only counted once. So the more spread out the players are, the more chunks will be covered and therefore the higher the maximum mob caps will be. The mob cap is checked once at the beginning of each spawning cycle. If the number of mobs in a category is over its cap, the entire spawning cycle for that category of mob is skipped. For each spawning cycle, a single attempt is made to spawn a pack of mobs in each eligible chunk. A random location in the chunk is chosen to be the center point of the pack, but for the pack to spawn at all, the center block must be water for water mobs and air for all other mobs. Note that in the previous case, it must be an air block. Any other block, even a non-colliding(sign, redstone, etc) one, will prevent the entire pack of mobs from spawning. If the pack location follows the previous guidelines, 12 attempts are made to spawn up to 4 mobs (8 for Wolves, 1 for Ghasts) within a 41x1x41 area centered at that block (that's a 41x41 square that is one block high). Mobs will spawn with the lowest part of their body inside this area. For each spawn attempt, a block within the area is chosen at random. Though the pack area extends 21 blocks out from the center, the random location is heavily skewed toward the center of the pack. Approximately 85% of spawns will be within 5 blocks of the pack center, and 99% within 10 blocks of the center. All mobs within a pack are the same species. The species for the entire pack is chosen randomly from those eligible to spawn at the location of the first spawn attempt in the pack: In the Overworld, this depends on the biome: Most biomes can spawn sheep, pigs, chickens, cows, spiders, zombies, skeletons, creepers, Endermen, slimes (in certain chunks), and Squid. Forest and taiga biomes can also spawn Wolves. Jungle biomes can also spawn Ocelots. Desert, beach, river, and ocean biomes cannot spawn animals; only hostile mobs and Squid. Mushroom biomes can spawn only Mooshrooms. Cave spiders spawn only from their specific Mob Spawners, which are found in Abandoned Mine Shafts among many cobwebs. Silverfish spawn from special stone, cobblestone, and stone brick blocks found in strongholds, and their specific spawners also found there. Blazes spawn from their specific spawners in Nether Fortresses and can also spawn elsewhere in the structures. The Nether itself can spawn only Ghasts, Zombie Pigmen,and Magma Cubes. The End can spawn only Endermen. The Ender Dragon spawns naturally in The End; but only one, ever; and not as part of the general mob spawning process. Now for each individual spawn attempt will only succeed if all of the following conditions are met: There must be no players and no player spawn points within a 24 block distance (spherical) of the spawning block If it's a squid, then... the spawning block must contain liquid (water or lava) the spawning block must be between level 45 and 62, inclusive the spawning mob must not be obstructed by other mobs If it's not a squid, then... the spawning block itself must be non-opaque and non-liquid the block directly below it must be opaque the block directly above it must be non-opaque the spawning mob must not be obstructed by blocks, other mobs, or water If it's an animal, then... the block directly below the spawning block must be grass the light level of the spawning block must be 9 or brighter if it's an ocelot, then... the spawning block must be above level 62 the block directly below the spawning block must be grass or leaves there is a 1/3 chance the spawn will fail If it's a hostile mob in the overworld, then... the light level of the spawning block must be 7 or darker, and more light increases the chance that the spawn will fail sunlight falling on the spawning block further increases the chance that the spawn will fail, by up to 50% If it's a slime, then... the spawning block must be in a chunk eligible to spawn slimes (see the Slime page for details) the spawning block must be below level 40 for medium and large slimes, the difficulty must not be set to peaceful Note: this condition is redundant as it is skipped completely on peaceful there is an additional 90% chance the spawn will fail, thus slimes only spawn 1/10th as often as other mobs, all other things being equal If it's a Ghast, then there is a 95% chance the spawn will fail, thus ghasts only spawn 1/20th as often as other mobs If all of these conditions are met then the mob is spawned. The pack is complete when 4 mobs have spawned (or 8 wolves, or 1 ghast), or 12 attempts have been made, whichever comes first. The only exception to these rules is the Enderdragon.