Slime

A slime is a green, sentient, 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. Slimes only appear in the bottom 16 layers of the map regardless of light levels or time of day, often in large caverns or open mines.

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

Sizes
Huge slimes do not spawn naturally and require modding to spawn. The small, normal and big slimes have equal chances of spawning (33%).

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

Unlike other hostile mobs, a slime will try to constantly path to the player if they are close enough, but when the player is far enough away, its movement becomes much slower, finally stopping when the player has exceeded the slime's awareness distance. In SMP, they path to the closest player and will only attempt to attack that player, ignoring other mobs and players even if attacked by them. Larger slimes are big enough to indirectly damage attacking wolves while attempting to attack a player. While tiny slimes do not directly damage the player, they can easily push them into other hazards such as lava. These tiny slimes are sometimes kept as pets because they will follow the player around.

Slimes cannot swim and drown if completely submerged in water and unable to jump out. They will burn upon contact with lava and die with enough exposure. Despite the lack of any limbs, slimes can climb ladders and follow the player out of caverns.

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. 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.

Slimes only require a 1x1x1 space to spawn in and that the block below this space is opaque and the block above it is a transparent block or air. They can spawn in any light level and lighting does not affect its 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).

Tiny slimes can spawn in Peaceful difficulty but all other sizes require Easy or harder difficulty settings. Slimes have equal chances to spawn at any size (and the selected size must be equal to Tiny for it to spawn on Peaceful difficulty). This means that if a slime that isn't the smallest size spawns in a 1x1x1 space, it will start to suffocate and split into smaller slimes. Slimes can spawn in spaces that already contain slimes.

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/

An online tool to find slime spawning chunks (by providing the world seed and a search region to test for slime spawning) can be found here: http://www.minecraftforum.net/topic/397835-find-slime-spawning-chunks/ (See image on right.)

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 bow, a wooden axe, a stone pick or a iron shovel (see: dealing damage), or simply punch the slimes. Drowning or suffocating slimes to death will also cause them to split or drop slimeballs, but slimes killed by lava or wolves will not.

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

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.

Trivia

 * The huge slime is the second largest mob in the game (only Ghasts are bigger), although SMP plugins can be used to create much larger slimes.
 * Slimes are notorious for causing severe localized lag in multiplayer when they split into several smaller entities.
 * 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.