King Slime is a large boss enemy that behaves like an oversized Blue Slime and can be fought at virtually any stage of a playthrough. He hops toward the player in a repeating jump pattern, summons smaller slimes as he takes damage, and will teleport to the player if they move too far away or if he cannot reach them. King Slime plays boss music, creates a boss health bar and map icon when active, and is unique among most bosses in that he can also be damaged by lava.
King Slime's movement follows a set sequence of jumps: two normal hops, a low jump, then a high jump. His highest jump can clear a 17-block-high wall. As his health decreases he becomes smaller and faster, and he spawns Blue Slimes; in Expert and Master Mode he additionally summons Spiked Slimes. The Blue Slimes dropped during the fight can drop Hearts and Mana Stars, restoring 20 health and 100 mana respectively, and they also drop Gel; King Slime himself does not drop Gel. Because many Blue Slimes are produced, summoning King Slime in specific areas is an effective way to farm certain enemy drops (for example, biome keys, Pirate Maps, Halloween/Christmas event items, and certain yo-yos such as the Cascade, Hel-Fire, Amarok, Yelets, and Kraken), as well as Gel for crafting or cooking.
King Slime will teleport to the player if distance or obstruction prevents him from dealing contact damage. Teleporting is preceded by a visible shrink and the boss map icon moving lower toward the ground, which can be used to anticipate his return when he vanishes offscreen. Teleportation can occasionally place him inside blocks, temporarily preventing movement until he teleports again. When teleporting he drops his crown and appears to generate a new one upon completing the teleport. In certain world seeds (For the Worthy) his body size is doubled in both width and height, and in Celebration Mk 10 worlds he can naturally spawn much farther from the world spawn than usual.
Practical notes for fighting and farming:
Use piercing weapons to hit King Slime and simultaneously damage or clear many of the Blue Slimes he summons. This is especially useful for rapid kill or farming runs.
Bring means of mobility and ranged options to avoid his high jumps and to maintain a safe distance so you can attack him without being crushed by contact damage; his damage is high for a pre-Hardmode boss.
Because Blue Slimes drop Hearts and Stars, fights can be sustained with life/mana recovery from their drops. Exploit this by fighting on flat arenas where pickups are easy to collect.
Summon King Slime in areas with desired rare spawn tables to farm those drops quickly; the high number of spawned slimes increases the chance to obtain event or biome-specific items.
Be aware that lava damages King Slime, making lava traps or arenas viable strategies against him (King Slime and Golem are the only bosses affected by lava in the usual ways).
Killing King Slime on Expert Mode and selling all drops yields a notable amount of coins on average.
King Slime occupies a unique place among bosses: he can appear randomly like normal enemies, can be repeatedly encountered after initial defeat, and is often treated as a side- or mini-boss despite full boss presentation. He has thematic ties to the Ninja armor via a trapped ninja found inside him and contributes several unique drops used by players in early to mid-game progression.
