Monster Spawner



Monster Spawners or Mob Spawners are blocks with a transparent dark grey lattice structure found in dungeons, Abandoned Mine Shafts, Strongholds and Nether fortresses. Inside the block there are flames that do not give off any light and a miniature spinning version of the mob that will spawn, which slowly increases speed until the next mob spawns.

Players have designed many traps to kill mobs from spawners, employing a long fall, drowning, lava, cactus or a combination of these, which allow the player to collect drops or experience in great numbers with little risk (see dungeon mob farming.)

The Monster Spawner is one of the few blocks not made available in Creative Mode.

Occurrences
Spawners may occur in these locations:


 * Dungeons
 * Spawning Zombies (50% chance), Skeletons (25%), or Spiders (25%). One per dungeon.


 * Abandoned Mine Shafts
 * Spawning Cave Spiders. Located in horizontal tunnels, surrounded by Cobwebs.


 * Strongholds
 * Spawning Silverfish. Located in End Portal rooms.


 * Nether Fortresses
 * Spawning Blazes. Located on balconies with stairs leading up to them.

No naturally occurring spawners will spawn mobs not on the above list, such as passive animals, Creepers, and Endermen; however, if a map editor or mod is used to create a spawner for any mob, it will function as expected.

There is no way to obtain a spawner in your inventory (even in creative mode), except using an Inventory Editor program or the `/give` operator command in a multiplayer server. If such a spawner is placed, or if a spawner is missing its tile entity data, it will spawn pigs.

Spawning Behavior
A spawner block will create mobs in the surrounding area, provided suitable spawning locations for the block's mob type can be found in the area. Spawning conditions vary from mob to mob. For example, Overworld monsters can only spawn in darkness (light level 7 or below), and animals must spawn on top of grass (light level 9 or above). However, spawner blocks can spawn mobs in mid-air, ignoring general rules about spawning on solid ground.

A monster spawner is only active when a player is within a distance of 16 blocks from the spawner (where distance is calculated the standard (euclidean) way). While the block is active, it will spawn mobs within an 8x3x8 block area (8x8 wide and 3 high), centered on the corner of the spawner block with the lower x and z coordinates. Mobs can spawn anywhere in this range that is suitable, even if the immediate vicinity of the spawner block itself is not suitable.

The block will spawn up to 4 mobs at once and then wait anywhere from 200 to 799 ticks (10 to 40 seconds) before spawning again. As it waits, the mob inside the block will spin faster and faster. If the block fails to spawn any mobs because it did not find any suitable locations, it will search constantly until it does. Only when it manages to spawn at least one mob will it start waiting for the next cycle. If, at the time of spawning, 6 or more monsters of the block's type are present within a 17x17x9 area centered on the spawner block, the spawner "poofs" without creating any monsters and then waits for the next cycle.

Note that, while mobs are spawned at a discrete y coordinate, the x and z coordinates are real-valued i.e. not aligned to blocks. Mobs will spawn with their legs at either the same level as the spawner block, one block above it, or one block below it. But horizontally, a mob can spawn with its center point anywhere within the 8x8 range. Since the mob itself takes up some horizontal space, this must be added to the range of the spawner to get the full dimensions of the area they can potentially occupy.

Spider spawners have the same 1% chance of spawning Spider Jockeys as natural spider spawning. Spawners can be given unusual entity IDs like Minecart or Boat to make a decorative block with the named entity spinning inside the cage which will not spawn anything.

In Peaceful difficulty, Monster Spawner blocks will still appear, but any spawned mobs will disappear the instant they spawn. This makes it easy to make the traps without being troubled by the mobs. The brief instant that the monster exists in the world before being removed is enough time for the player to be pushed around and, in some cases, for the sound file to play.

Detailed Spawning algorithm
This pseudo-code is derived straight from the decompiled source of Minecraft Beta 1.7.3. every spawn cycle (every randInt(200,799) ticks when a player is in range of the spawner), loop 4 times { if there are 6 or more of the mob type in the 17x9x17 area around the spawner, skip this spawn cycle calculate spawnerX = X coordinate of center of spawner - 0.5 calculate spawnerY = Y coordinate of center of spawner - 0.5 calculate spawnerZ = Z coordinate of center of spawner - 0.5 calculate x coordinate of mob = spawnerX + (randDouble - randDouble) * 4, randDouble being a random number between 0 and 1 calculate y coordinate of mob = spawnerY + a random whole number between -1 and 1 calculate z coordinate of mob = spawnerZ + (randDouble - randDouble) * 4, randDouble being a random number between 0 and 1 if all of the conditions specific to the mob type are met, spawn the mob { chicken, cow, pig, sheep, wolf: block below spawning block is grass spawning block has a light level of 9 or higher

slime: difficulty is not set to peaceful or slime size is small (if it's not peaceful, the algorithm won't get to this point) spawn block y coordinate is less than 40 the chunk containing the spawn block is a slime chunk (1 in 10 chance) pass a 1 in 10 random test ghast: pass a 1 in 20 random test squid: must not collide with any other entities

all except squid and slimes: must not collide with any other entities must not collide with any blocks must not collide with water or lava } }

Trivia

 * Monster Spawners are destructible with an Iron Pickaxe as of Minecraft 1.1. It is not known if this is also possible in the Overworld or with inferior Pickaxes.
 * Due to a bug, all Mob Spawners found in SMP have pigs inside them instead of whatever creature they actually spawn.
 * Monster Spawners can spawn monsters in a nearby cave, even when the monster spawner appears fully lit, due to its 8 x 8 x 3 spawn radius.
 * The model inside the monster spawner has an ID number like all other mobs, though it is only visible at certain angles and cannot be seen since Beta 1.8.
 * Since monster spawners are stored as tile entities, they cannot be pushed by pistons.
 * It is possible for a monster spawner to occur near the surface and completely buried in sand, with monsters spawning in small gaps underneath sandstone.
 * Unlike most other transparent blocks, it is possible to place torches on a monster spawner.
 * Before the first Beta 1.9 Pre-release, the texture of the cage was lighter.
 * In 1.9 pre-releases 4 and 5 it was possible to obtain a Monster Spawner using a tool enchanted with Silk Touch. When placed they would only spawn pigs. Silk Touch was made ineffective on spawners in Beta 1.9 pre-release 6.
 * If a Monster Spawner is destroyed in SMP by a server process (e.g. TNT) the box will be deleted, but the flames inside will remain, until the client/player logs off and back onto the server.
 * It is possible for two Monster Spawners to naturally occur directly side-by-side.

Spawning
 * When mining near a monster spawner that has no valid places to spawn, sometimes a monster will spawn immediately after a block is mined. The player should take caution for this reason while collecting Moss Stone from a dungeon but hasn't destroyed the monster spawner.  It's speculated this might happen because the spawner gets a chance to spawn before the lighting calculation for the space the block occupied.
 * A monster spawner may spawn 1, 2, 3 or even 4 mobs at once

The miniature mob inside the spawner
 * If you are not within range, the miniature mob inside the spawner will stop spinning, and the mob spawner will stop emitting fire particles.
 * The miniature mob model displayed inside the monster spawner was enabled again in Beta 1.2 after being missing for several versions.
 * The miniature mob inside the mob spawner will spin faster when it is about to spawn monsters. There are set minimum and maximum speeds for which the miniature mob can rotate.

Hacking spawners
 * If a spawner is hacked to create Ghasts, Giants, Squid, Slimes, Endermen or Enderdragons (Giant spawners don't spawn anything), the model inside will be miniaturized, but not enough to fit the cage properly, because the scaling factor used is the same as with other mobs.
 * The squid spawners seem to have stopped working since 1.9 prerelease 5.