Spawn

Spawning refers to players and mobs being created and placed in the game world.

World spawn


New players initially spawn within a small area surrounding the world spawn point when the server is not in adventure mode. This area is 21×21 blocks by default, but can be changed by the  gamerule in both single and multiplayer. Upon death, the player respawns within this area unless the player's individual spawn point changed (by sleeping in a bed or using a respawn anchor). In addition, the player can only spawn on grass blocks in the world spawn.

When the player loads into the world or respawns, the game searches within the world spawn area and places the player on a grass block. Any non-solid such as string, carpet, and flowers that are placed directly above a grass block causes the block to become a invalid spawn point. If all grass blocks are removed or have non-solid blocks, the player will spawn directly in the center of the 21x21 area.

Upon spawning, the player is placed on the highest block of the X and Z spawn coordinates, even if this would set the player above the maximum build height. This area does not consider the existence of a block to spawn on, which can result in players spawning above the Void if there are no blocks at that X and Z location.

The world spawn point also determines the center of the permanently loaded spawn chunks.

The world spawn point itself can be changed using the command.

Bedrock world spawn search
$$, when a player creates a new world, the world spawn point is restricted to specific biomes. The algorithm starts searching from coordinate 0,0 continuing outward until an acceptable biome is found for the world spawn point. Using add-ons, a rare biome can be designated to cause the player to spawn at a distant location, but the game crashes if the biome does not exist or cannot generate.

The algorithm searches for these biomes:
 * At main plains biome
 * Small islands in an ocean (islands are usually a plains biome)
 * Patch of plains next to desert, badlands, or snowy tundra
 * At main forest biome
 * Small islands in an ocean (islands can also be a forest biome)
 * At main taiga biome
 * Patch of taiga next to giant tree taiga
 * Near beach, snowy taiga, or mountains
 * Only regular variants
 * At main taiga biome
 * Patch of taiga next to giant tree taiga
 * Near beach, snowy taiga, or mountains
 * Only regular variants
 * Only regular variants
 * Only regular variants

The player spawns within a 5 block radius of the point selected in the chosen biome, sometimes resulting in the player spawning outside the spawn biome, ending up in a beach, river, or swamp biome.

A search for a valid world spawn biome is not performed for Flat and Old world-types.

Adventure mode
When the server's settings set the default game mode to adventure mode (using the server.properties), then the normal spawning mechanic is ignored and players are spawned directly on the world spawn. This includes the X, Y and Z coordinates, even if there is no block there and even if there are blocks above it.

If the Y coordinate is not a valid spawning area then the server looks up until it finds one, up to a maximum of Y=256. If there is space to spawn but it is in midair, the player spawns in midair, even falling into the void if there is a hole.

Location
There are several ways to determine the world spawn point:
 * A compass (that hasn't been assigned to a lodestone) always points to the spawn point.
 * Doing the commands then.
 * Entities other than players falling into the exit portal in the End land on the exact spawn point. Items thrown in mark the spot in the Overworld. Players spawn like they normally do, allowing this to be used to perform the above without dying.
 * Mods or external programs such as NBTExplorer or MCEdit can also be used to find and set the world spawn point.

Individual spawn
The individual spawn point of the player can be changed by sleeping in a bed, using a respawn anchor, or using the command. If the individual spawning area of the player is obstructed upon death, the player respawns at the world spawn.

Sleeping in a bed allows for leniency in obstruction, in that the player respawns on other blocks near the bed if the original point becomes blocked. The same is true for the respawn anchor. If the spawn point set via becomes obstructed, the player is not given this leniency in respawning.

Natural generation
Many mobs generate upon initial chunk creation. These spawns occur only once per chunk. They are not affected by the command.

Animals


Approximately one in ten newly generated chunks contain mobs, usually in packs of up to four of the same species. They always spawn on the highest available block in a column. For an animal to spawn on it, this block must be opaque and the two blocks above it must be transparent. The block does not need to be a grass block nor does it need to be illuminated as it does with mob spawning.

There are 2 types of animals: common animals and biome specific animals.

Common animal mobs do not spawn in desert, badlands, beach, snowy tundra, river, ocean, and mushroom fields biomes. The weight is the spawn rate for the bedrock codebase.
 * Common animals
 * Weight: 6, 2-3 animals
 * Weight: 5, 2-4 animals
 * Weight: 5, 1-3 animals
 * Weight: 4, 2-3 animals
 * Weight: 5, 1-3 animals
 * Weight: 4, 2-3 animals
 * Weight: 4, 2-3 animals
 * Weight: 4, 2-3 animals

Some animal mobs spawn only in specific biomes.
 * Biome specific animals

Randomness for animal spawning is derived from the world seed, which means that worlds with the same seed always generates chunks with the same animals in the same places.

Monsters
Most monsters cannot spawn on peaceful difficulty. At higher difficulty, most of them prevent the player from sleeping, and most of them spawn at light level of 7 or less.


 * Common monsters

Common monster mobs can spawn in almost any biome in the Overworld (except for mushroom fields). They can spawn on the surface and underground. The weight is the spawn rate in the Bedrock Codebase.
 * Weight: 100, in groups of 2-4
 * Weight: 100, individually
 * Weight: 100, individually
 * Weight: 80, in groups of 1-2
 * Weight: 10, in groups of 1-2
 * Weight: 5, individually
 * Weight: 80, in groups of 1-2
 * Weight: 10, in groups of 1-2
 * Weight: 5, individually
 * Weight: 10, in groups of 1-2
 * Weight: 5, individually
 * Weight: 5, individually


 * Biome-specific monster

Some monsters spawn only in specific biomes.

Other mobs
These mobs still spawn if the command is set to , because they spawn as part of structure generation.
 * Villagers, iron golems, stray cats, pigs, cows, sheep, and horses generate as part of the village generation.
 * Specific animals spawn as part of specific village structures: Animal pens (cow, sheep, pig, or horse), stables (horse, cow, or pig), butcher's houses (pig, cow, or sheep), and shepherd's houses (sheep).
 * Each villager spawns in a house with a bed, and an iron golem spawns as part of meeting points.
 * Zombie villagers can spawn as part of zombie village generation, where they never despawn naturally.
 * Cats also spawn upon generation in abandoned villages.
 * A single witch and black cat spawn within a swamp hut upon generation.
 * Three elder guardians generate as part of a single ocean monument.
 * A single ender dragon is created in the End when the dimension is created. The ender dragon can also be respawned by placing end crystals on the exit portal.
 * Shulkers generate as part of end cities.
 * Vindicators and evokers generate as part of woodland mansions and high level raids.
 * A villager and a zombie villager generate as a part of an igloo if it generates with a basement.
 * Drowned generate as part of some underwater ruins.
 * Illagers spawn from pillager outposts, raids, and patrols.
 * Phantoms spawn whenever a player hasn't slept for 3 or more days.

Java Edition
Mobs are broadly divided into four categories: hostile, friendly, water (e.g. squid), and ambient (e.g. bat). Hostile mobs have a spawning cycle once every game tick ($1/25$ of a second). Friendly and water mobs have only one spawning cycle every 400 ticks. Because of this, where conditions permit spawning, hostile mobs spawn frequently, but passive mobs (ie: animals) spawn rarely. Most animals spawn within chunks when they are generated.

Mobs spawn naturally within a square group of chunks centered on the player, 15×15 chunks (240×240 blocks). When there are multiple players, mobs can spawn within the given distance of any of them. However, hostile mobs (and some others) that move farther than 128 blocks from the nearest player despawn instantly, so the mob spawning area is more-or-less limited to spheres with a radius of 128 blocks, centered at each player. In multiplayer, mob caps are shared by all players, no matter where they are.

Every 24000 ticks (20 minutes) the game attempts to spawn a single wandering trader with two leashed llamas within 48 blocks of a player or at a village meeting place, if no wandering trader exists in the world. The trader does not spawn when the player is underground.‌

Java Edition mob cap
Mob caps are directly proportional to the total number of chunks eligible for spawning. To calculate the cap, the spawning area is expanded by one chunk in every direction (so the default gives 17×17 chunks), then the total number of chunks is plugged into the following formula:

mobCap = constant &times; chunks ÷ 289

The constants for each group are as follows:
 * Monster = 70
 * Creature = 10
 * Ambient (bats) = 15
 * Water creature (squid, dolphins) = 5
 * Water ambient (fish) = 20
 * Misc = -1

The "misc" category is only used by entities that are not mobs, do not spawn naturally, and/or following different spawning rules than other mobs. As such the mob cap has no bearing on mobs of this category.

In singleplayer, there are always 289 chunks in range so the constant is always used as the global mob cap.

In multiplayer, the global mob cap grows as more chunks are loaded. As chunks that are in the range of multiple players are counted only once, more chunks and higher mob caps result from the players spreading out more.

The number of mobs is checked once at the beginning of each spawning cycle against the cap. If the number of living mobs in a category is over its cap, the entire spawning cycle for that category is skipped. The area checked for mobs is the same as the area used for calculating the mob cap, which is the spawning area expanded by one chunk in every direction. The mob cap count is separate for each dimension.

The check for if a mob can spawn relies on greater than, meaning when no more mobs will spawn is mobcap+1.

Pack spawning


For each spawning cycle, attempts are made to spawn packs of mobs per each eligible chunk. An eligible chunk is determined by the same check for which chunks are random ticked. A random location in the chunk is chosen to be the center point of the pack. If the block which a pack spawn occurs on in an opaque full cube, further pack spawn attempts are cancelled.

The pack is spawned within a 41×1×41 (that's a 41×41 square that is one block high) area centered at the initial block. Mobs spawn with the lowest part of their body inside this area. For each spawn attempt, from the location of the previous attempt a location up to 4 blocks away from the previous attempt is chosen at random. Thus, the spawns are heavily skewed toward the center of the pack. Approximately 85% of spawns are 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, but biased on a weight system from those eligible to spawn at the location of the first spawn attempt in the pack.

The game checks on each spawn if the number of mobs that have been spawned for the pack is equal to the max spawn attempts.

Pack spawn attempts max out at:


 * 8 Wolves, cod, bats and tropical fish
 * 6 Horses and Donkeys
 * 1 Ghast
 * 4 for any other mob

When the max pack size is less than the number of possible spawn attempts, some spawns attempts will fail, but will be seen more commonly in practice. Based on the number of mobs which have been successfully spawned. If the max pack size is greater than the number of spawn attempts, you will only only get the number of spawns from the spawn attempts. Some mobs have a minimum and max pack size, meaning there is an even chance for any number of spawn attempts between them occurring.


 * For Zombie Villagers, Drowned, Pillagers, Donkeys in savanna biomes, Parrots in Jungles excluding Bamboo Jungle and Jungle, cats in Witch Huts and Witches it is 1
 * For Parrots in Bamboo Jungle and Jungle, Polar Bears, Squids in Lukewarm Ocean, Panda s and Dolphins it is 1-2
 * For donkeys in plains biomes, ocelots and pufferfish it is 1-3
 * For Enderman except in The End and in nether wastes, and Squids except in Lukewarm Ocean it is 1-4


 * For Rabbits and Blazes it is 2-3
 * For Guardians, Foxes, Zombified Piglin in Crimson Forest and striders it is 2-4
 * For Turtles it is 2-5
 * For Horses it is 2-6
 * For Piglins and Hoglins in Crimson Forest it is 3-4
 * For Cod it is 3-6
 * For Llama it is 4-6
 * For Mooshrooms, it is 4-8
 * For Wither Skeletons and Skeletons in nether fortresses it is 5
 * For Bats and Tropical Fish it is 8
 * For every other mob it is 4

For all dimensions, bounding boxes take priority over biome for hostile spawns. This means that in a witch hut, pillager outpost, nether fortress (outer bounding box only when there is nether brick below it), and ocean monument you will see only the corresponding hostile mobs for that structure within that structure.

In the Overworld, this depends on the location:


 * Jungle biomes have a higher chance to spawn chickens.
 * Badlands biomes spawn only hostile mobs and bats.
 * River and frozen river can spawn only drowned, squid, and salmon underwater.
 * Ocean biomes do not spawn passive mobs. They spawn drowned, and the other hostile mobs. Frozen oceans do not spawn dolphins, but do spawn polar bears.
 * Witch huts spawn only witches, cats, and bats.
 * Ocean monuments spawn guardians, other water mobs and bats.
 * Pillager outposts spawn pillagers, other passive mobs and bats.
 * All other overworld biomes spawns common animals and common monsters, as well as slimes, dependent on spawn conditions.

In the Nether, the locations are less varied:
 * Skeletons, wither skeletons, magma cubes, zombie pigman and blazes can spawn within Nether Fortresses.
 * Ghasts can spawn in nether wastes.
 * Zombified Piglin and Piglin can Spawn in nether wastes, while magma cube spawn primarily in Basalt Delta biomes and sometimes in nether wastes.
 * Mobs (excluding zombified piglin and skeleton) that can spawn anywhere in the Nether ignore light level.
 * Hoglins and Piglins and can spawn at a higher rate anywhere in the Crimson Forest biome.
 * Endermen can spawn more frequently in the Warped Forest biome, but not in crimson forest.
 * Skeletons and Ghasts can spawn more frequently in the Soul Sand Valley biome.

Spawn conditions
Note that whether a spawn condition will fail differs from the above determination if the game will try to spawn them in that biome. For example, dolphins can have pack spawns occur inside of frozen ocean and deep frozen ocean biomes, but no other biomes. These rules apply to variants of the same mob, such as baby zombies and spider jockeys.

Each individual spawn attempt succeeds only if all of the following conditions are met:
 * There must be no players and spawn points (player spawn point or world spawn point) within a 24 block distance (spherical) of the spawning block
 * The number of loaded mobs of that type must be less than the mob cap for that type. (I.e. the corresponding mobcap must not be full)
 * The mob's collision box upon spawning must not collide with another collision box. A mob cannot spawn inside of anything that would collide with it upon spawning.
 * The mob cannot spawn if any block where the collision would reach is a block which powers redstone or is a full cube.
 * For all mob types excluding passives, spawns will fail unless within a 128 block sphere around the player.
 * Gamerule DoMobSpawning is true

Hostile mobs:


 * The difficulty must not be peaceful
 * For all hostiles other than guardians and drowned:
 * the block directly below it must have a solid opaque top surface (this includes upside down slabs, upside down stairs, top trapdoors and others) or be soul sand or a slime block
 * the block directly below it must not be bedrock, barrier or any type of trapdoor.
 * the spawning block and the block above that cannot be rails, powered rails, detector rails, activator rails, redstone components, wither roses (except for wither skeletons) or sweet berry bushes (except for foxes).
 * The mob's collision box must not touch any liquid.
 * For slimes from swamp biomes, creepers, skeletons, wither skeletons, witches, zombie villagers, husks, strays, drowned and spiders:
 * The light level divided by 8 is the chance of a spawn failing from light level, thus mobs spawn at light level 7 and below
 * In the overworld, this follows internal skylight level as well as block light level. Internal light level is affected by thunderstorms
 * Spawns with sky access have an additional 50% failure rate
 * If it is a slime from a swamp biome, then.....
 * the spawning block must be in a swamp biome
 * the spawning block be on level 51 through 69 inclusive
 * chance of failure based on the phase of the moon
 * 50% chance of failure
 * If it is a husk or stray, then....
 * The location of the spawn must have skyaccess, generally determined by having a skylight level of 15.
 * If it is a skeleton in a Nether fortress, then...
 * there is an 80% chance of spawning a wither skeleton instead
 * If it is a drowned, it will:
 * have a $1/5$ chance to succeed in oceans, while a $8/10$ chance to succeed in rivers
 * In ocean biomes, drowned spawn at a height less than 5 blocks below sea level
 * The light checks in the general hostile mob check don't apply to:
 * Slimes from slime chunks (see the slime page for details), which spawn when:
 * the spawning block is be below level 40
 * with a 90% chance of failure
 * Ghasts, which spawn:
 * With a 95% chance of spawn failure
 * Magma cubes
 * The block the mobs spawns on cannot be nether wart
 * If it is a zombie pigman then...
 * the light level must be 13 or lower
 * Hoglins
 * Piglins
 * If it is a blaze, then...
 * the light level must be 11 or darker
 * If it is a polar bear, then.....
 * The light level must be greater than 8
 * The block beneath must be ice
 * The spawning block must be in a frozen ocean or deep frozen ocean
 * If it is a blaze, wither skeleton, skeleton, magma cube or zombie pigmen in the fortress external bounding box
 * the block beneath must be nether bricks

Passive mobs:


 * If it is an animal then...
 * if it is not an ocelot or strider, the light level of the spawning block must be 9 or brighter
 * If it is a mooshroom, then.....
 * the block directly below the spawning block must be mycelium
 * If it is a turtle then.....
 * the block directly below the spawning block must be sand
 * the spawning block must be level 67 or lower
 * For all others then.....
 * the block directly below the spawning block must be grass
 * If it is an ocelot, then...
 * the spawning block must be level 62 or higher
 * the block directly below the spawning block must be grass or leaves
 * there is a $1/10$ chance for the spawn to fail
 * If it is a strider, then.....
 * Spawn attempts with lava above will check upwards as long as there is still lava for if they can successfully spawn in a lava block with air on top
 * Striders will spawn at y level 31 or lower

Aquatic mobs (squid, a guardian, a drowned, a cod, a salmon, a pufferfish, a tropical fish or a dolphin:


 * the spawning block and the block below must be liquid (water) or be waterlogged
 * the block above the spawning block must be either transparent or non-solid (I.e. doesn't occupy a full cube)
 * If it is a squid, then...
 * the spawning block must be between level 46 and 62, inclusive
 * the spawning block must be in an Ocean or River
 * If it is a dolphin then.....
 * the height of the spawn must be greater than 45 and less than sea level (62).
 * the spawning block must be in an ocean or deep ocean
 * If it is a guardian, then...
 * the difficulty must not be peaceful
 * 95% chance of failure if the spawning block has sky exposure (details)
 * If it is a cod, a salmon, a pufferfish, a tropical fish, then.....
 * the block above the spawning block must be water (excluding waterlogged blocks)
 * the block which it would spawn must not be waterlogged

Ambient mobs:


 * If it is a bat, then...
 * the spawning block must be at level 62 or below
 * If the real-time day is between October 20 and November 3, then the light level must be 7 or darker. Otherwise the light level must be 4 or darker.

If all of these conditions are met then the mob is spawned.

Bedrock Edition
Natural spawning $5/10$ shares some similarities to natural spawning in Java Edition. In Bedrock Edition, there are two main types of natural spawns: pack spawns and structure mob spawns. Structure mob spawns are mobs spawned as part of a structure, such as nether fortresses, witch huts, etc. Pack spawns account for all other types of natural spawns, including mobs that spawn individually (i.e. not in a pack of 2 or more). Both types of natural spawns follow the same rules for spawn conditions and the mob cap, however most animals can spawn at light level 7 or higher rather than 9 or higher.

Mob spawning is evaluated for every chunk within a 6 chunk cylindrical radius of the player that is ticked; if the simulation distance is smaller than 6 chunks, then only chunks within the simulation distance can spawn mobs. There is a $4/10$ chance of the mob spawning algorithm attempting to run per chunk, per tick.

Bedrock Edition mob cap
There are two main mob caps that affect spawning: a global mob cap and a mob density cap. The global mob cap for natural spawns is set at 200 regardless of difficulty. The global mob cap affects only natural mob spawning, and does not affect mobs spawned through breeding, spawn eggs, the command, monster spawners or any other type of mob spawning. Only mobs that are within ticking areas (both those around players and those set manually using the command) count toward the global mob cap; mobs not ticked do not count toward the global mob cap. Mobs can also have their own individual cap listed below:

Alongside the global mob cap is a mob density cap. The mob density cap limits how many mobs of each type and category can spawn within a 9 chunk by 9 chunk square region surrounding each chunk eligible for spawning. Mobs in chunks outside a ticking area still count toward the mob density count. The density cap is split up into two distinct categories: a cap for surface mobs, and a cap for cave mobs. Cave mobs do not count toward the surface mob cap, and surface mobs do not count toward the cave mob cap. Whether a mob counts as a surface mob or a cave mob is determined by where it spawned, not where it happens to be at the moment.

There are four categories of mobs: ambient, animal, monster, and water. The mob density cap for each category and location of mob in each dimension is as follow:

Spawn conditions
The following rules apply to all mobs:
 * Can spawn only between 24 and 54 blocks spherical radius from the player.
 * Cannot spawn if the block below them is air (except for Phantoms).
 * Cannot spawn if that mob would collide with an existing mob.
 * Cannot spawn on bottom half of slabs or carpet.

Some additional rules apply to specific categories of mobs.

For water mobs:
 * Cannot spawn outside of liquid.

For monsters:
 * Cannot spawn if the light level is greater than 7.

For non-water mobs:
 * Cannot spawn on bedrock or invisible bedrock.
 * Cannot spawn touching any liquid.

Pack spawning
Pack spawning happens in two stages: first attempt to spawn surface mobs, then attempt to spawn cave mobs. Before spawning, the mob density cap is calculated based on the 9x9 square area surrounding the current chunk. Spawning begins by picking a random X and Z location within the chunk currently being evaluated. The Y coordinate is determined by starting at the world height and searching downward for the next block of a certain type with a non-solid block above it. The first such block that is found is considered to be the surface, and the algorithm attempts to spawn a surface mob pack. The algorithm then continues to search downward for the next suitable block with a non-solid block above it. When a block meeting the criteria is found, the algorithm attempts to spawn a cave mob pack at that block location. Cave spawn attempts continue until the Y coordinate reaches the world bottom, and do not stop even if a cave pack was spawned.

Surface and cave pack spawn attempts then go through the following steps to figure out what mob to spawn and how many:


 * 1) Picks a random mob.
 * 2) * If the current spawn location is in a liquid, pick a random water mob.
 * 3) * If the light level is greater than 7, there are no other blocks above the current location, and the current location is a grass block, pick a random animal mob.
 * 4) * Otherwise, spawn a monster mob.
 * 5) Picks a random number of mobs to spawn in the pack. Each mob can have its own min and max pack size, and the pack size can depend on difficulty.
 * 6) Make sure the spawn location has suitable spawn conditions.
 * 7) Limit the number of mobs spawning based on the global mob cap. No mobs spawn if the mob count already meets or exceeds the mob cap.
 * 8) For each mob to spawn, check that spawning it would not exceed the mob density cap.
 * 9) * If spawning the mob would not exceed the mob density cap, then the probability of a mob spawning can be calculated using the formula:
 * 10) Finally, attempt to spawn the mob in the world.
 * 11) * Spawning the mob can fail; for example, if spawning it would cause it to spawn inside of a block or part of a wall.

Other types of spawning

 * Cows, chickens, pigs, sheep, mooshrooms, villagers, ocelots, wolves, horses, llamas, donkeys, rabbits, pandas, cats, foxes, turtles, bees, striders, and hoglins can breed. All of these require a player to breed them except for villagers.
 * A thrown egg will spawn chickens. See: Egg Chicken Spawning
 * A snow golem, iron golem, or wither can be made to spawn if a player builds the proper structure out of blocks. Iron golems can also spawn in sufficiently populous villages. See their respective pages for full details.
 * An infested block spawns a silverfish if broken, or if a nearby silverfish is attacked.
 * Zombies can spawn in large groups in villages at midnight if the player is within the village, ignoring some of the usual restrictions, forming a siege. The game makes 20 attempts to spawn a zombie within a 17×17×17 area centered on a block within the village's cylindrical radius, at the same Y level as the village center.
 * Zombie pigmen can spawn from nether portals in the Overworld. Lighting and player proximity don't prevent this.
 * Endermites can spawn randomly when a player uses an ender pearl.
 * Killing medium and large slimes and magma cubes spawn more of them, but in a smaller size.
 * When a pig gets struck by lightning, it is replaced by a newly spawned zombified piglin.
 * When a villager gets struck by lightning, it is replaced by a newly spawned witch.
 * If a creeper gets struck by lightning, it becomes charged.
 * A monster spawner causes mobs to spawn constantly in the area around it. Spawners may naturally generate spawning zombies, skeletons, spiders, cave spiders, silverfish, magma cubes, or blazes, but may be made to spawn other mobs using commands or spawn eggs. See: Spawner
 * Turtle eggs hatch and spawn baby turtles.
 * Zombies, illagers, and zombie pigmen can spawn reinforcement when hurt.
 * Trapped horses can spawn during thunderstorms, then spawning skeleton horsemen.
 * Zombie villagers spawn as 5% of naturally-spawning zombies
 * A villager killed by a zombie has a 50% chance of becoming a zombie villager in normal difficulty, and 100% chance in hard difficulty.
 * Skeletons spawn as 20% of naturally-spawning strays.
 * Zombies spawn as 20%/30% of naturally-spawning husks.
 * Baby zombies, zombie pigmen, drowned, husks, and zombie villagers have a 15% or 5% chance of spawning as chicken jockey.
 * Spiders and cave spiders have 1% chance of spawning as spider jockey
 * Vindicators, evokers, pillagers, ravagers, and witches can spawn as part of raids.
 * Phantoms spawn after player does not sleep or die for at least 3 days.
 * Cats spawn based on the number of beds in a village.
 * A brown mooshroom spawns when a red mooshroom is struck by lightning, and vice versa.
 * Patrols consist of vindicators and pillagers. $1/10$, patrols can spawn like regular monsters. $8/10$, patrols can spawn in any biome except in the End, the Nether, and mushroom fields; they even spawn in biomes where common monsters cannot spawn, such as in legacy frozen ocean.
 * Cod, salmon, pufferfish, and tropical fish spawn when using the corresponding bucket of fish.
 * Bees spawn when a bee nest or beehive is broken without silk touch.
 * If a piglin or hoglin is transported to the Overworld or the End, after 15 seconds they will transform into zombified piglins or zoglins, respectively.
 * In Creative or via a dispenser, the player can use spawn eggs to spawn most mobs. When mobs are spawned this way, all normal spawning requirements, such as light level and block type, are ignored. (Though monsters other than vindicators, evokers, shulkers, and ender dragon still cannot be spawned in peaceful)
 * An agent spawns when using a code connection.
 * Any entity can be spawned using the command.

Java Edition


Hostile mobs (other than villagers that were converted to zombie villagers or witches), chickens from chicken jockeys, monsters, despawnable mobs (including bats, squid and ocelots) (after having existed for over 2400 ticks), and hostile wolves can cease to exist, or "despawn", under certain conditions:


 * A mob that has had no player within 32 blocks of it for more than 30 seconds has a $8/10$ chance of despawning on each game tick ($5/10$ of a second), which is a 2.47% chance per second. Therefore, the average lifetime of monsters not within 32 blocks of a player is 40 seconds (after the initial 30 seconds have elapsed).
 * A mob despawns immediately if no player is within 128 blocks of it, or 54 blocks.
 * Note that this is a Euclidean sphere, not a cylinder from map top to bottom and not a taxicab sphere (which is more like an octahedron). Example: A mob at 0/y/0 remains at least 30 seconds (as above) if the player moves to 65/y/65 (real distance 91.9), but despawns immediately if the player moves to 91/y/91 (real distance 128.7).
 * The chunk the mob is in must still be loaded to the mob to despawn. Otherwise, the mob is saved until the chunk is loaded again.
 * All hostile mobs (including those that are holding items) in a world despawn if the difficulty is set to Peaceful, regardless as to where the player is positioned in the world.
 * In multiplayer, despawning does not occur while there are no players in the game.
 * A monster that has been named with a name tag never despawns. However, one created from a renamed spawn egg does despawn as normal.
 * If a monster holds any items or wears any armor that was given by a player or picked up from the ground, it does not despawn.
 * Chickens that originally spawned as chicken jockeys follow zombie despawn rules, rather than chicken despawn rules.

Persistence
$4/10$, entities with persistence do not despawn naturally. Entities are given persistence in the following situations:


 * The entity interacts with a player:
 * Is ridden by the player.
 * Is named with a name tag.
 * Is tempted with food.
 * Is bred, or born as a result of breeding.
 * Is tamed by the player
 * Using the command.
 * Curing a Zombie Villager (spawns a Villager).
 * Triggering a skeleton trap (spawns Skeletons and Skeleton Horses).
 * The entity is spawned during the generation of a certain kind of structure:
 * Shulker spawned in an End City.
 * Witch spawned in a Witch Hut.
 * Villager or Zombie Villager spawned in an Igloo.
 * Zombie Villager Spawned in A Zombie Village.
 * Vindicator spawned in a Woodland Mansion.

The following entities always have persistence:
 * Ender Dragon
 * Wither Boss
 * Elder Guardian
 * Guardian
 * Iron Golem
 * Snow Golem
 * Villager
 * Armor Stand
 * Agent
 * Ender Dragon

1.16 Changes
$1/10$ Bedrock Edition spawning and despawning has been changed to match Java edition more closely.


 * Almost all naturally spawning mobs will now despawn when they're 44 blocks or further away from the nearest players in a world with simulation distance 4. On higher simulation distances, mobs are despawned when they're in a chunk at the edge of the simulation distance up to a distance of 128 blocks from the nearest player.
 * All fish will despawn at a max range of 40 or more blocks on all simulation distances.
 * If mobs are between 32 and 44 blocks from the nearest player, they must not take damage for 30 seconds as well as succeeding a 1 in 800 chance to despawn.

Trivia

 * In older versions, it is possible for the spawn point of a world to be in a lava lake, in which case starting a game in Survival is nearly impossible unless there is water nearby. This was fixed in 1.9, so that lava lakes fail to generate in the world spawn area.
 * The world spawn (the point where players spawn if they have no valid bed spawn) is usually a random (seed determined) point between -500 and +500 on the X and Z axis. If the chosen point is in water (due to nothing but ocean biomes in the -500 to +500 range), a second attempt is made between -1500 to +1500. If this fails due to ocean, the game gives up and puts the world spawn in the middle of the ocean (still at the surface) (attempting to play the flat lands preset Water World does this, for example). Normally, a player who spawns in the water does so near the shore because the world spawn itself picked a spot there.
 * An opaque block normally causes all blocks below it to spawn cave mobs, but not if a transparent block is placed on top. This can be exploited for [ certain mob farms].