Slime Monsters

Slimes are a very common set of monsters, identified as slightly transparent blobs that slowly hop toward the player in an attempt to attack. It is the most common enemy in Terraria, able to spawn at any time of day and in nearly every biome.

Slimes come in a multitude of colors, including blue, purple, green, red, yellow, and black. There are other variations such as Mother Slimes, who are a larger form of Black Slimes, and when defeated spawn several Baby Slimes. Upon being slain, Slimes drop coins and gel, the latter can be used to create torches, sticky Bombs, potions, and sticky glowsticks.

Slimes are the biggest threat to new players, due to them Bombarding the player almost immediately and wasting valuable time if they kill the player. However, Slimes on the surface will pass you by if you do not attack them while Slimes underground are more aggressive.

As of 1.0.5, they float on water instead of sinking. This may allow players to escape attack by hiding underwater.

On the surface, Slimes are neutral during the day and will jump across the level minding their own business. However, attacking them will cause them to become aggressive and will become aggressive when night falls. Slimes found in caves are always aggressive. Because of this, and reports that jungle slimes don't attack during the day, there is reason to believe that lack of sunlight turns Slimes hostile. Despite their size, all Slimes (excluding the Mother Slime and King Slime) can fit through a 1 block high space.

In earlier versions of the game, the Slime spawn rate was stated by Blue to be far beyond reasonable, leading the developers to tone down the spawn rate to something more subtle. Blue dubbed the never-ending onslaught as the "Slimepocalypse".

Strategy
Slimes' movement and tactics are very simple, being limited to hopping in one direction with short pauses between each leap. The simplest way to avoid slimes is to block their path. Placing wood platforms at a natural choke point is a reasonable alternative since Slimes cannot fall through them. You can tell they are about to jump by looking. Just before they jump they appear to be shaking. If they are bothering you and you dont feel like killing them, set a couple lava pools around your town so they will jump in it and kill themselves. This strategy also works on Zombies. Make sure you put some block in front of a NPCs door so they dont wander into the lava pool!

Special Slimes
The Black Slime is one of the enemies that inflicts the darkness debuff which decreases the night vision, (the others being the Demon and the Voodoo demon). A large black slime found in deeper caves, the Mother Slime is 3 blocks wide and 2 blocks tall, making maneuvering in tight areas more difficult. Upon death, it splits into two or three smaller and weaker 'Baby Slimes'. Using a weapon with a large area of effect and high damage, such as a flail, large sword, or explosives, is an efficient way to dispatch the Mother Slime and its "offspring" at the same time.
 * Black Slime
 * Mother Slime

A tiny pink slime found on or near the surface which has 150 health. On death, it drops 60-100 Silver Coins.
 * Pinky

A boss randomly spawned in areas with lots of grass. For it to spawn, you must be 1/3 of the map length away from your original spawn. Being further away from spawn increases your chances of King Slime spawning. There is no known way to summon it. It has 2000 health, and drops a piece of the Ninja outfit when killed. It can jump so high that it will leap off screen on the highest resolutions, but it doesn't always jump this high.
 * King Slime

Dubbed the strongest non-boss slime in the game, the lava Slime only exists in Hell, and also is the only slime invulnerable to lava. Plus it can jump twice as high as any other Slime in the game (excluding King Slime) and can also change directions in the air, making getting away from it very difficult. As of the 1.0.6 patch, it will no longer drop lava on death.
 * Lava Slime

Habitat-Based Differences
Green and blue Slimes spawn regularly on the surface during the day. Purple Slimes also spawn on the surface, although less frequently. Pinky is the last surface-dwelling Slime and has the rarest spawn rate.

During the day, all of these Slimes are happy to ignore you as long as you do not attack them first. However, if they are spawned already when night arrives, they will become hostile to you. None of these Slimes spawn above ground during the night.

Blue, red and yellow Slimes spawn in the dirt layer fairly regularly, with Pinky also spawning rarely as well. Red and yellow slimes are always hostile, while Blue Slimes and Pinky are sometimes willing to ignore you until attacked.

Jungle Slimes are common but spawn only exclusively to surface jungles. Jungle Slimes will start jumping towards you as soon as they appear on your screen. However they do not spawn at day. Being the strongest common Slime they become quite a hassle when trying to explore a jungle.

Dungeon Slimes are uncommon and only spawn inside of the Dungeon. They are always hostile and will attempt to jump at the player if at elevation. They also have a 100% chance of dropping a Golden Key, which can be used to open Dungeon Chests.

Black and Mother Slimes spawn regularly in the stone layer, as well as rarely in the outer Underground Jungle biome, becoming rarer the deeper into the biome you travel. As with red and yellow Slimes, black and Mother Slimes are always hostile on spawn. Baby Slimes, which spawn as a result of killing Mother Slimes and look like black Slimes, are also always hostile.