This event is very dangerous for early game players due to the high spawnrates of enemies.

If the Eye of Cthulhu has never been defeated, the event still becomes available once Hardmode begins.

After the player has defeated the Eye of Cthulhu, the Acid Rain is guaranteed to begin the next time they visit the Sulphurous Sea.

Other weather events such as the Blood Moon can overlap with the Acid Rain event.The event's enemies will override the Sulphurous Sea's enemies, similarly to Meteor Heads.While the Acid Rain event is active, Rain will be active across the rest of the world.Sulphurous Crates will contain Corroded Fossils, Belching Saxophone, Flak Toxicannon, Nuclear Fuel Rod, Skyfin Bombers, Slithering Eels, Spent Fuel Container, and Sulphurous Grabber.Acidwood Trees will contain Corroded Fossils when shaken.Sulphurous Crates will contain Sulphuric Scales.Acidwood Trees will contain Sulphuric Scales when shaken.The following is a list of enemies in the Acid Rain event and the amount of points gained from each enemy per kill. The event can also be prematurely ended with a Torrential Tear. If the player doesn't kill any enemies within the time span of four minutes, the event will automatically cancel and progress is reset for the event. In Multiplayer, the number of points required is calculated by the expression (amount in singleplayer) * ln(total players + e - 1)), rounded down, based on how many players are in the world at the start of the event. To complete the event, the player must gain 90 points in the first tier, 115 in the second, and 140 in the third.

Unlike other weather events, the Acid Rain has a progress bar and can be completed.

Calamity mod