King Slime

King Slime is a boss that is, as its name would suggest, a very large slime: It is roughly 15 times larger than the Dungeon Slime (the largest ordinary slime). It is summoned with the Slime Crown, and 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!"

King Slime is considered a mini-boss in that it is a large and resilient enemy (and Boss music plays while fighting it), but it is not a required step to advance the game. King Slime can be encountered regardless of the current level of advancement, and defeating it does not provide access to any critical items. It also does not travel through blocks, which creates shielding possibilities for the player that don't exist when battling other Bosses.

Random spawning
Aside from using the Slime Crown, King Slime will also spawn randomly based on the following conditions:


 * King Slime only spawns during the Day, above 0 depth, and on grass-covered Dirt blocks.
 * King Slime randomly spawns only in the two outer thirds of the map (the far left or far right). An easy way to determine if you are far enough is to check for the presence of bunnies, which spawn only in the inner third of the map, surrounding your original spawn point. If you can see bunnies, you are not far enough from your spawn point.
 * 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.
 * Possibly can spawn from killing large amounts of slimes (Wire based machine is the best way to accomplish this)(Unproven)

Under these conditions, King Slime has a 1 in 300 chance to spawn. 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 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 relativity easy, due to the fact that the blue slimes it spawns drop stars, which refill 100 mana.


 * King Slime, unlike other slimes, does not skip along the water surface, but instead sinks. To avoid being swarmed by the slimes he spawns, consider luring him into a lake.


 * Advanced players can build an arena for farming Tattered Cloth 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.


 * Shurikens are a good weapon, they can hit King Slime and the Blue Slimes multiple times.

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.
 * This is the only boss (besides the Wall of Flesh) that does not have a hardmode version.
 * The King Slime is the only slime that doesn't use the slime AI.
 * It is possible for King Slime to spawn inside of holes too small for him to escape, making it very easy to defeat.
 * Out of the five Pre-Hardmode bosses in the game, King Slime does the second most damage out of all of them, not counting Skeletron's arms, and is surpassed by only the Wall of Flesh.