|AI Type||King Slime AI|
- Internal NPC ID: 50
- 1 Spawn Condition
- 2 Battle
- 3 General Strategies
- 4 Specific Strategies
King Slime can be spawned by fulfilling any of these conditions:
- Rarely in the outer lateral sixths of the map, during daytime, and only on grass, replacing a normal Slime's spawning;
- Naturally by Natural-occurring Slime Rain;
- Using Slime Crown.
It must then be defeated before all the involved players die.
King Slime is no different than a normal Slime: it moves by hopping to the player. Unlike other Slimes, however, it has a large pool of health due to its Boss status, and it's huge. This makes King Slime an easy target, but he jumps far and unpredictably; the height varies depending on the distance between him and the player. Failing to predict its jump destination can result in the player getting damaged.
Getting too far away from King Slime will make it teleport to the player, meaning that the player cannot escape by simply running off the screen. However, this can be taken advantage of, as it can get stuck in enclosed spaces.
As King Slime gets damaged, it gets smaller. This makes it more mobile and harder to hit, having less issues to escape small enclosures (should it fail, however, it might teleport instead), and it spawns lesser Blue Slimes to harass the player. These can make the player waste ammo on them instead of the King Slime, so the use of piercing weapons or ammo is important.
Old-gen console and 
The main difference between these versions with Desktop, Console, and Mobile is that it does not teleport; it can be eternally stuck in small to medium-sized enclosures if it spawns there, but is mostly the same.
There are not many changes about the King Slime itself besides its higher Damage and Health. However, when damaged it will spawn Spiked Slimes in addition to regular Blue Slimes. Those can throw volleys of spikes at a short distance, so having a weapon which can pierce multiple targets and attack from a range will be necessary to avoid being bombarded to death.
King Slime is one of the few bosses in the game that lack the ability to go through blocks. This can be exploited in multiple ways:
- On Console version, climbing on a Rope 35 blocks above the ground allows the player to attack him at range safely without him teleporting onto the player. Add extra rope to give the player a margin of error, or to retreat and heal if need be. Using this method makes potions, higher damaging weapons, armor, and movement accessories optional, as the player will not need to dodge attacks or mitigate damage.
- Make one or two platforms above the ground; King Slime will eventually teleport to ground level and the player can easily hit him from the platforms.
- A flat area with small room below it with Platforms as roof for the player. King Slime can't enter small rooms and thus cannot reach the players in it.
It is possible to exploit the King Slime's large size in Old-gen console and versions by making him stuck in-between blocks.
It is also good to place Campfires and Heart Lanterns, as they increase the player's health regeneration. A Star in a Bottle and a Sunflower can also help increase mana regeneration and movement speed respectively.
Defense: Gearing Up
Armor is not very important in this fight. However, it is recommended to have at least Cactus Armor, as it is easy to obtain and provides a decent amount of defense. More armor is always better. However, in Expert or Master Mode, better armor is recommended due to King Slime's buffed HP and attack power.
Summoners are recommended to get the Flinx Fur Coat.
Most weapons can be used to fight this boss without difficulties. Piercing weapons may be preferred, to hit both the Blue Slimes and the King Slime himself.
- As a Melee character, basic metal swords are a bad idea due to the amount of Slimes the King will spawn, but the Enchanted Sword, Ice Blade, Terragrim (or Arkhalis in the Console version) or Starfury should definitely be used if obtained.
- An Enchanted or Ice Boomerang is great at attacking him from a distance. The Flaming Mace and Chain Knife are similar options.
- The Storm Spear, obtained in the Underground Desert, is another early projectile weapon that works well.
- The Rally is also helpful. If the player is willing to adventure into the Underground Jungle, the Amazon is a great choice.
- Rangers should bring a Gold or Platinum Bow. ADemon or Tendon Bow can also be used, if the player already defeated Eye of Cthulhu or was lucky to find Demonite or Crimtane Oreand mine it with a Gold, Platinum Pickaxe or any other pickaxe with over 50% Pickaxe power.
- Frostburn Arrows or Jester's Arrows are the preferred ammo type, due to the high single target damage of the former and the piercing effect of the latter.
- The Snowball Cannon is another strong ranged weapon.
- All guns are very effective against King Slime, although they require breaking a Shadow Orb or Crimson Heart.
- Sticky grenades do the most damage in pre-hardmode, so they are a good choice, but they do not stick to bosses
- Magic users should bring at least Sapphire. TheEmerald staff, Ruby Staff or Diamond Staff are the best staves available.
- Summoners should bring either a Vampire Frog Staff, a Flinx Staff or a Finch Staff, and a Leather Whip if affordable.
- The Snapthorn is also a good choice, better than the leather whip
- If the player has only acquired the Slime Staff, one may use it.
- Thrower should bring a bunch of Throwing Knives or Javelins. Grenades can deal a lot of damage, although they may damage the player if used recklessly.
Like weapons, most accessories can help:
- Sailfish Boots, Hermes Boots, Flurry Boots, Dunerider Boots or a Panic Necklace can assist with avoiding damage or running away in bad situations. These should be combined with Rocket Boots at the Tinkerer's Workshop if the Goblin Tinkerer has been rescued.
- The Flying Carpet is also a very good accessory since its ability to hover can make the King Slime unable to reach the player.
- Cloud in a Bottle, Blizzard in a Bottle, Sandstorm in a Bottle, Fart in a Jar, or Rocket Boots (if the player have defeated the Goblin Army) can also help with any vertical movements. If one has a Shiny Red Balloon, they should combine it with a bottle accessory, making it even better.
- Lightning Boots are really hard to get, but can be incredibly useful
- A Band of Regeneration can be useful to increase rate of regeneration while avoiding being damaged by King Slime, and a Mana Regeneration Band can help to refill Mana faster.
- A simple multiple-platform arena is best, because it gives you good mobility and you waste less recourses
- Campfires are a great choice because they give health regeneration
- if you are at full health, Heart lanterns are also a good choice, though this is a stretch because you need 1 life crystal.
- Star in a bottle is a good choice for mages, especially because fallen stars are more common
- Bast statues are also a good choice, and are good all throughout the game, though are hard to find, especially because it is located in the Underground Desert
- Having the Nurse living on your arena is a good choice, mainly because King slime cannot go through blocks, and the health is nice to have, and she removes any debuffs
- Ironskin Potions can help by reducing the damage received.
- Regeneration Potions help recovering life lost.
- Any food that grants the Well Fed, or any other high up buffs from food.
- Swiftness Potions to better evade the teleports and run under the jumps if needed.
- Archery Potions are a good choice because you can find them in chests underground and give a good buff to rangers.
No teleports Strategy
- Build a one-block thick wall 18-20 blocks high;
- Create a walkway between 35-50 blocks long with platforms for maneuverability;
- Make sure a Campfire is nearby.
- Use any long-range weapons (Yo-yos, Bows, Gem Staves or Throwing weapons).
- Make a minecart track-above the typical platform where the player summon king slime-and put bumpers on the end, King slime will have a hard time trying to teleport to the player because the player is moving super fast.
Lava pit Strategy
Because the King Slime can be harmed by Lava, a good strategy is to use a Lava Bucket to make a long strip of land with a small amount of lava (shallow enough so items don't burn) and then make some widely placed platforms. the player can jump, use rocket boots, or use a grappling hook to move between platforms. Just be careful to not jump in the lava if the player don't plan to use Obsidian Skin Potions. This strategy works with his teleports, and the minions will all die from falling in the lava. The player doesn't have to focus on fighting, because the lava will dish out major damage. The player can also skip the platforms, and use a Obsidian Skin Potion, and just evade by running under the slime, or use Rocket Boots to fly over.
Another strategy is to make something that could help the player later, a long Minecart rail path. If the player build it just high enough, he will not be able to teleport or jump on the player. His attacks rely on the player being on the ground. To the AI, it seems that the player are on the ground, so he just sits under the player and occasionally jumps, making him an easy target.
Death Box Strategy
In Console, Old-gen console, and , upon the player's death, the King Slime will attempt to travel off-screen in order to despawn. However, the King Slime cannot travel through solid blocks, so he can easily be trapped in a small area until death.
- A solid box must be constructed. The box should be large enough to hold the King Slime, yet not so large that he can still wander off-screen.
- A bed should be placed within the box. In order to make the bed usable, it may be easiest to build a small cubicle within the box to hold the bed.
Before the King Slime spawns, the player should be inside the box with his spawn set on the bed. Once the King Slime awakens, he will teleport within the box to attack the player. The player should deal any damage he can to the King Slime at this time. The King Slime should inevitably kill the player and attempt to hop off screen. However, he will find himself trapped in the box and will not be able to leave. The player will respawn at the bed and is free to deal any additional damage to the King Slime before his next death. Repeat this process until the King Slime is defeated.
Since this strategy revolves around the player's death, hardcore players should avoid implementing this strategy.