Slime

A slime is an animate, green, gelatinous cube that can appear in various sizes and will follow the player around if they come close enough. The larger slimes can split into smaller ones under certain conditions and will hurt the player upon contact. 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. As of Beta 1.9 Pre-release 5, they can now spawn up to layer 40.

Usage
A tiny slime will yield 0 - 2 slimeballs upon death. Slimeballs are a key ingredient of sticky pistons and magma cream.

Sizes
All slimes have an equal chance of spawning.

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.

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. They can also climb ladders, and be pushed over slabs but not 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 only spawn in certain chunks that are determined pseudo-randomly by the seed of the world the player is in, and only below layer 16 (as of 1.9 pre 5 this is no longer true since they now can spawn up to level 40). Roughly 10% of all the chunks will be able to spawn slimes, based on the formula:

Random rnd = new Random(seed + (long) (xPosition * xPosition * 0x4c1906) + (long) (xPosition * 0x5ac0db) +             (long) (zPosition * zPosition) * 0x4307a7L + (long) (zPosition * 0x5f24f) ^ 0x3ad8025f); return rnd.nextInt(10) == 0;

That is, Java's random number generator is first seeded by the number seed + (long) (xPosition * xPosition * 0x4c1906) + (long) (xPosition * 0x5ac0db) + (long) (zPosition * zPosition) * 0x4307a7L + (long) (zPosition * 0x5f24f) ^ 0x3ad8025f, 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 coordinates (xPosition, zPosition) is able to spawn slimes. Multiplying the chunk coordinates by 16 will give the player coordinates since a chunk is 16x16.

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

Like most other mobs, Slimes require two vertical non-opaque blocks(e.g., glass or air) to spawn in, with an opaque block underneath. However, the usual collision check that comes after this is skipped for Slimes. As a result, Slimes can spawn in spaces that are too small for them, inside transparent blocks like glass, and inside other mobs. If a non-tiny slime spawns inside an opaque block, it will suffocate and split into smaller slimes.

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. In addition to this, slimes have 90% less chances of being picked for spawning compared to the other 4 hostile mobs (creeper/skeleton/spider/zombie).

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 sphere radius of any player. Similarly, slimes will despawn after some time if no player is within 32 meters sphere radius of it, and despawn instantly if no player is within 128 meters sphere radius.

The slime spawning algorithm is explained in greater detail here: http://www.minecraftforum.net/topic/385523-slime-spawning/

Splitting
Larger slimes will split into 4 smaller slimes that are each one size smaller, if and only if the killing blow causes no overkill damage. This means that the player can use a tool that does the gcd of all the splittable slimes' health, such as a wooden axe, a stone pick or a iron shovel (see: dealing damage), or simply punch the slimes. A bow was also a good weapon to kill slimes until it was updated with the release of 1.8. Drowning or suffocating slimes to death will also cause them to split or drop slimeballs, but slimes killed by lava or wolves will not. Since 1.9 prerelease, slimes always split upon death even if they take overkill damage.

Tiny slimes do not split and drop 0-2 slimeballs on death (they can be overkilled).

As of Beta 1.9 Pre-release 6, slimes can split into 2 - 4 smaller slimes.

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.

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


 * Note: Since 1.9pre5., slimes are no longer limited to 0-16 depth, but to 0-40.

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 to a huge slime, the arrow will also turn into a big arrow.

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 and Puddings from Nethack. The name and the large, cartoonish face may be an 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.