Slime

A slime is an animate, green, gelatinous, hopping, and relatively rare mob in the shape of an ordinary cube that can appear in various sizes. They will follow and attack a player who comes close enough. When killed, a slime will split into smaller slimes, except for the smallest slime which will drop slimeballs instead. Slimes are found only in the lowest 40 layers of the map, and only in certain areas. Slimes can spawn in a flatland because world generation level is 3 blocks above bedrock. Slimes are also planned to spawn above ground in Jungle Biomes in 1.2.

Usage
A tiny slime will yield 0 - 2 slimeballs upon death. Slimeballs are a key ingredient of sticky pistons, and can be used as an ingredient in the brewing of potions.

Behavior


Slimes move by hopping. They will always hop toward the closest player within 16 blocks (spherical) distance, even if they can't see that player. If no player is in range, they will simply hop in a straight line in whatever direction they were left facing. When they first spawn, they are facing in a randomly chosen direction.

Tiny slimes deal no direct damage to the player or other entities, but can push them, occasionally into lava or other hazards. The larger slimes cause damage on contact proportional to their size.

Slimes can take damage in all the usual ways: burning, falling, drowning, suffocating inside blocks, being attacked, falling into The Void, etc. When slimes are killed, they will split into 2-4 slimes of the next size down. Tiny slimes will not split, but will drop 0-2 slime balls on death. Slimes can even decay farmland.

In shallow water, slimes can hop fast enough to fight the current, as long as their hopping is not obstructed by a low ceiling. They will sink in deep water and won't be able to hop while submerged. And if they stay submerged for too long, they will die. They can also climb ladders, and be pushed over slabs and stairs.

While big and small slimes make a wet slapping noise, tiny slimes create the same sound as a player would walking on the block they are hopping on. Larger slimes make a splattering sound distinct from their movement noises when damaging a player. Slimes do not grow larger or smaller over time.

Spawning
Slimes spawn only below layer 40, and only in certain chunks that are determined pseudo-randomly by the seed of the world. Roughly 10% of chunks will be able to spawn slimes, based on the formula:

Random rnd = new Random((long) seed                        + xChunk * xChunk * 0x4c1906L                         + xChunk * 0x5ac0dbL                         + zChunk * zChunk * 0x4307a7L                         + zChunk * 0x5f24fL                         ^ 0x3ad8025fL); return rnd.nextInt(10) == 0;

That is, Java's random number generator is first seeded by the value (long) seed + xChunk * xChunk * 0x4c1906L + xChunk * 0x5ac0dbL + zChunk * zChunk * 0x4307a7L + zChunk * 0x5f24fL ^ 0x3ad8025fL, then the random number generator is asked to generate its first random number between 0 to 9. If this number is equal to 0, the chunk with coordinates (xChunk, zChunk) is able to spawn slimes. To convert world coordinates to chunk coordinates, divide by 16 and round down.

Tools exist to calculate which chunks are slime chunks—see.

Like most other mobs, Slimes require two vertical non-opaque blocks (e.g., air, signs, torches) to spawn in, with an opaque block underneath. The space they spawn in must also be clear of solid obstructions and liquids. Big Slimes require a 3x3x3 space to spawn, Medium Slimes require a 3x3x2 space, and Small Slimes require a 1x1x2 space (or 1x1x1 if the upper block is not opaque). Slimes are equally likely to spawn at all sizes. Slimes are much more likely to spawn in a 3 high room.

Slimes spawn only 1/10th as often as other hostile mobs, so they can be hard to find. Slimes can spawn in any light level and lighting does not affect their spawn rate. However, lighting up the surrounding area does decrease the chances of non-slime mobs spawning and thus indirectly increases slime spawning rates.

Slimes have equal chances to spawn at any size. They do NOT spawn in peaceful mode.

Like any hostile mob, slimes will not spawn within 24 meters (spherical) of any player. Similarly, slimes will despawn after some time if no player is within 32 meters, and despawn instantly if no player is within 128 meters.

The slime spawning algorithm is discussed in greater detail in this forum topic, but note that the algorithm has changed many times and older information may no longer be accurate.

Farming
Once a slime spawning chunk has been determined the process of encouraging slime spawning is relatively simple. The player can proceed in clearing out large rooms - typically 3 x 3 x 3 or larger - and should light them as to prevent the spawning of additional unwanted mobs. Waiting for slimes to spawn in these rooms can be lengthy at times, however. See the Slime spawning page on minecraftforum.net mentioned above for more information on how to increase this rate.

A similar method can also be used to players intending to play the game "legit" and avoid resorting to tools and mods. The player can simply go down the below the maximum height allowed for slime spawning and strip mine a cavern. Approximately 10% of chunks will spawn slimes, so the cavern must be fairly large to have a good chance of finding one. A cavern that spans 7 chunks has a 50% chance of including one that produces slimes; 22 chunks must be excavated to reach a 90% chance. This method is not recommended but does work.

Once slimes are found there are many ways to kill them. For smaller slimes the simple but effective, attack them with a sword, approach is found best but when up against larger slimes to use flint and steel to light the blocks between you and them, they will then move towards you and set themselves ablaze and break into more slimes.

Setting slimes on fire has become a popular method of getting slimeballs because the chances of the slimeballs burning is surprisingly low so through the use of netherrack setting parts of rooms where slimes spawn on fire is a great way to farm slimeballs.

Slime Finding Tools


These tools can be used to find chunks that are eligible to spawn slimes:

http://mcslimes.appspot.com/ (Java applet)

http://extension.ws/minecraft/slimes.html (HTML/JavaScript)

http://www.minecraftforum.net/topic/472121-173-slime-chunk-finder-10/ (in-game mod)

Rei's Minimap is also able to show this kind of chunks by highlighting them.

What's My Light Level can also aid players in finding Slimes.

Minecraft X-Ray, since version 3.4.0 (external map-viewer, not a mod)

AMIDST Finds Slime chunks as well as Strongholds, Villages, and Biomes. (external program)

History
Slimes were the fifth hostile mob added to the game on July 23, 2010 (Seecret Friday 6! Alpha 1.0.11). Notch limited slime spawning shortly afterwards because they would appear in abundance. A miscalculation in the new limit caused slimes to only spawn in strange locations, so Notch then disabled natural slime spawning.

Small slimes started to drop 0 - 2 slimeballs in Beta. Notch confirmed in Coestar's livestream that slimes had been reskinned and returned in Beta 1.2_01 but were still very rare. Slimes became more common in Beta 1.3  A bug remedied in Beta 1.5 caused slimes to spawn in Peaceful mode and attack without any provocation. An SMP bug fixed in Beta 1.4 caused slimes that split to be visible only to the player that caused them to split and would not take any damage. Because these slimes were client-side, the player could only remove them by exiting and logging back into the server.

Since 1.9 prerelease, slimes always split upon death even if they take overkill damage. Before Beta 1.9 Pre-release 5, Slimes only appeared in the bottom 16 layers of the map regardless of light levels or time of day, often in large caverns or open mines.

Bugs

 * Slimes are notorious for causing severe localized lag in multiplayer when they split into several smaller entities.
 * Slimes in SMP sometimes display as the wrong size, so it is often the case that you take damage from what looks like a harmless tiny slime.
 * Slimes in SMP often animate strangely, jittering up and down, and in some servers, disappear altogether sometimes(but can still be attacked and attack), though this is not always the case.
 * When you shoot an arrow at a huge slime, the arrow will appear like a large arrow.
 * Slimes can go through glass
 * If a slime is killed, and the user logs out before it despawns, upon returning it will be red and sideways, as if it's about to despawn, but resume hopping at the player.
 * Slimes don't go up when in water so they drown.

Trivia

 * Third party software can be used to create arbitrarily large slimes.
 * Slimes may have been inspired by a number of classic gaming monsters. Their shape and size resemble that of Gelatinous Cubes from Dungeons & Dragons (though admittedly that probably comes more from Minecraft's cubic art design than as a direct homage), and their splitting behavior resembles that of Zols from The Legend of Zelda, Puddings from Nethack and Ameboids from Ratchet and Clank. The name and the large, cartoonish face may be a homage to Yuji Horii's iconic Slimes from the Dragon Quest series.
 * Slimes will only attack the player, even if a skeleton accidentally shoots it.
 * There's a line in the code that's meant to allow tiny slimes to spawn on Peaceful, but the natural spawning algorithm skips hostile spawning entirely on Peaceful. As a result, this line won't even be reached. However, there are illegitimate ways to spawn tiny slimes on Peaceful, e.g. with a Slime Monster Spawner.
 * Magma Cubes, added in Beta 1.9, could be seen as the Nether equivalent of Slimes.
 * The block a Slime is standing on will drip green liquid if looked at from below, similarly to lava and water.
 * Slimes hop faster when pursuing a player.
 * Despite Slimes being hostile mobs, many players have tiny Slimes as pets since they follow and can't directly damage players.
 * Before Beta 1.7, when peaceful was turned on, slimes would not despawn.
 * In Minecraft 1.1, when you create a world with the world type as "Super Flat", an excessive amount of Slimes will spawn. Slimes are extremely common since the level of the land is so low, which creates an extreme challenge for a player in survival mode.