Slime Rain is an event from Terraria, now ported to Minecraft. You can start a Slime Rain event by using a Slime Crown, which you can buy from the Wandering Trader (who also sells Lesser Healing Potions).

After using the Slime Crown on the ground, slimes will fall from the sky in batches, a message also pops up. The more slimes you defeat, the more slimes will fall.

The slimes

Green, blue and purple slimes are the variants that will appear in the event, with the green one being the standard Minecraft slime. All these slimes are slightly stronger and drop emeralds.

There's also a chance for Pinky to spawn. Pinky is a tiny pink slime with more health than any of the other slimes.

King Slime

Once you have defeated a good number of slimes, King Slime will spawn. You can tell when the message pop up appears.

King Slime is as slow as the other slimes, but has a lot of health and deals more damage. King Slime will drop emeralds, gold and healing potions, and also has a chance to drop the King Slime Trophy, a trophy you can use as decoration.

Other details about the add-on:

• Despite being a fairly easy event you can complete early on, the increasing number of slimes can overwhelm you. Be sure to bring armor!
• Be very cautious of where you're standing, you'll never know when 1 or 2 or 15 slimes will suddenly fall on you.
• Be sure to pick up the loot, as these might cause your device to lag, along with the high number of slimes.
• King Slime is very tanky and cannot be knocked back, but can be kited easily, so get rid of all the other slimes first.