Slime Rain

Slime Rain is a minor event that lasts for one in-game day or night, and consists of frequent Green, Blue, and Purple Slime spawns. Near the conclusion of the event, the King Slime boss will spawn if you had killed 150 slimes during the event. If the King Slime has been previously killed, it only takes 75 slime kills for him to spawn. The event ends if King Slime is killed. Upon completing the event, the player receives the "Sticky Situation" achievement

This event can happen simultaneously to a Blood Moon, the two series of monsters spawning together.

During Slime Rain, the background appears to contain falling slimes, and Slime enemies will fall from the sky near the player. The Slime spawn rate is greatly increased, which provide a good chance to harvest Pink Gel, and many bonus items that slime can carry.

Trivia

 * The background slimes will fall vertically if the player stands still. If the player moves left, the slime rain will fall at an angle pointing slightly left and the same applies to moving right.
 * There is a small chance for Pinky to spawn during the event.