King Slime

The sky jiggles above you...

King Slime is a boss that is, as its name would suggest, a very large slime: It is roughly 5 times larger than the Rainbow Slime (the largest ordinary slime). It is summoned with the Slime Crown, but can also spawn on its own rarely (but never in the center third of the map). As the King Slime takes damage, it spawns additional ordinary Blue Slimes. It will always drop one piece of Ninja clothes when defeated.

When King Slime spawns, a message appears in the bottom-left corner of the screen that reads: "King Slime has awoken!" Upon defeat, a similar message appears: "King Slime has been defeated!"

It is immune to the Poisoned debuff.

Random spawning
King Slime has a 1 in 300 chance of spawning in place of another slime while the player is located in the two outer thirds of the map (the far left or far right).


 * Goblin Scouts spawn in the same locations as the King Slime, so you'll know if you're in the right place if you encounter any.
 * A Water Candle and/or the Battle Potion can speed up the process of encountering it.

Strategy

 * King Slime behaves exactly like a normal slime, except that he jumps much higher and further, and spawns other slimes after being hurt by the player. Due to its predictable nature, it is easy for a new player to defeat the boss with even lower tier weapons. The only thing a new player should worry about is dodging the King Slime as it jumps about, as he deals a relatively large amount of damage per hit. To finish the boss quickly, projectiles such as Boomerangs, Shurikens, Spiky Balls, or Bows and Arrows are recommended.
 * Digging a pit two blocks wide and three blocks deep is an excellent tactic for fighting the King Slime, which is too large to fit in such a small pit. Placing wood platforms on top of the pit has the added benefit of keeping the smaller slimes out.
 * King Slime's absolute highest jump can clear a 17-block-high wall, so if you're planning on trapping him somewhere, make your walls at least 18 blocks high.
 * Fighting the King Slime with magic is relatively easy, due to the fact that the blue slimes it spawns drop stars, which refill 100 mana.
 * Advanced players can build an arena for farming Tattered Cloth, Slime Staff, and Ninja clothes. Build a base on where Goblin scouts are spotted, make sure that there are no pools of water on either side of that point and there are no caverns below, because goldfish, slimes and goblin scouts may spawn on those crevices. Have a lava moat on each side of your base, while making sure that the lava is low enough not to destroy any items dropping in it. Have Battle Potion consumed and equip a Water Candle to increase chances of King Slime and Goblin Scout to spawn.
 * A strategy using the Crimson Rod (or Nimbus Rod if you have access to one, because it's essentially the same thing but deals three times more damage) involves digging a pit low enough to conceal the player. Place a cloud above the pit and it will damage king slime as well as destroy any slimes that fall into the pit with the player. If done right the player will not have to do anything else.
 * A great way to take the King Slime out very easily is to find above or exactly his jump height, then stand upon a platform. Afterwards you can fire anything at the boss to take him out fairly quickly without taking any damage.

Trivia

 * Given the presence of the ninja inside, the king slime may be a reference to Ninja Gaiden, in which one of the first bosses is a slime-like creature that devours you.
 * The King Slime is the only slime that doesn't use the slime AI.
 * It is one of the few pre-hardmode bosses that doesn't have a hardmode robotic counterpart.

History
史萊姆之王