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. Upon being slain, Slimes drop Coins and Gel, the latter can be used to create Torches, Sticky Bombs, Potions and Sticky Glowstick. Slimes are the biggest threat to new players, due to them bombarding the player almost right away and wasting valuable time if they kill the player. Although, slimes on the surface will pass you by if you do not attack them, while slimes underground are more aggressive.

A recent blog post by Blue states that, as of 1.0.5, they will float on water instead of sinking. This may allow players to escape attack by hiding underwater.

Slimes are neutral during the day and will jump across the level minding their own business but attacking them will cause them to become aggressive. They will become aggressive when the night falls. Slimes found in caves are always aggressive. 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 neverending 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, as slimes cannot fall through them.

Special Slimes
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.
 * 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


 * King Slime

A boss randomly spawned in caves and in areas with lots of grass. For it to spawn, you must be 1/3 of the map length away from your original spawn (This is written in the code). 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 so high.


 * Lava Slime

Dubbed the strongest non-boss slime in the game, the lava slime only exists in hell, and also is the only slime invurnable to lava, knowing that, the lava slime also drops lava on death! 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.

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, so long as you don't attack them first. However, if they are spawned already when night arrives, they will become hostile to you. None of these slimes spawns 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 they do not spawn at day. Being the strongest common slime they become quite a hassle when trying to explore a jungle.

Black and Mother Slimes spawn regularly in the Stone layer, as well as rarely in the outer Underground Jungle biome (becoming more rare 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.