Heavy Rain is a weather event in the Betweenlands. Every once in a while, it will rain very heavily in the dimension. This rain has the same effect as it does in the Overworld. In addition, it will cause Puddles to generate in large masses on opaque blocks exposed to the sky.
Heavy Rain can be manually triggered using the following command: /blevent <toggle/on/off> thebetweenlands:heavy_rain