Slime

A slime is a green, sentient translucent gelatinous cube that appears in various sizes and splits into smaller slimes under certain conditions and will follow the player around if they come close enough. With the exception of the smallest specimens, slimes 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
Each tiny slime yields 0 - 2 Slimeballs upon death. Slimeballs do not currently have any use, but tentatively in Beta 1.7, they will be a component of sticky pistons.

Slime Farming
Slimes need a large, open space near the bedrock layer to spawn in. Create a room 5 blocks high with a 9 by 9 block floor close to the bedrock layer and cover the walls with torches to prevent other kinds of mobs from spawning. Slimes may spawn in particular chunks and not in others - this is determined when the world is being generated, and chunks that will spawn slimes cannot be found without the aid of external software.

Gather slimeballs by using 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). 1 huge slime is equivalent to 4 big slimes, 16 small slimes, or 64 tiny slimes for a total of 0 - 128 possible slimeballs.

Behavior
Slimes tend to remain around walls and corners, even if there is wide open space in the middle. While huge, big, or small slimes will make a wet slapping noise, tiny slimes 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 over time. While tiny slimes do not directly damage the player, they can easily push them into other hazards such as lava. These tiny slimes are often kept as pets by because they will follow the player around.

Combat
Slimes are relatively benign and slow-moving, but can be a moderate challenge to confront in groups (or in larger sizes). When hit, a huge, big, or small slime will break into four smaller slimes, unless it is killed with a weapon that deals at least more damage than its health. For example, causing a total of 8.5 hearts of damage to a big slime will cause it to die and anything below that will cause it to split. A stone sword should be sufficient to take care of all types of slimes.

Defensive Measures
Slimes of any size will burn upon contact with lava and die without splitting. Wolves attacking a slime will also not cause it to split. Slimes cannot swim and drown if they are completely submerged in water and will be unable to jump out. They do, however, have the ability to climb ladders and follow the player out of caverns.

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 later completely disabled natural slime spawning.

Small slimes would drop 0 - 2 slimeballs in Beta. Notch confirmed in Coestar's livestream that slimes has 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 if SMP plugins are used, slimes much bigger than Ghasts can be spawned.
 * 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.