Rain

The Rain is a timed environmental hazard deadly to the player and all other creatures. It appears at the end of every cycle once the in-game timer has run out. It is preceded first by a darkening of the screen and then by rumbling and screen-shake. These effects increase in intensity as the first drops of rain appear. The rain quickly increases in intensity until it is lethal, either crushing or drowning all creatures in affected rooms.

To avoid this hazard, the player must seek shelter.

Variation of rain
The arrival of the Rain has different effects depending on the room. In most outdoor rooms, the Rain directly impacts the player's movement, most severely in areas with no overhead cover. The Rain kills the player faster depending on its strength. In most indoor rooms, the Rain causes flooding which can drown the player. In particular areas such as Five Pebbles, the upper limits of The Wall, Sky Islands's Communications Array, the lowest subregion of Subterranean (Depths), the Metropolis and any shelter, the Rain does not appear.

In case of Metropolis, the Rain is instead replaced by a unique day/night cycle, with a lot more dangerous enemies appearing after the end of the cycle.

In The Leg and The Underhang, the green sparks floating around the area accelerate and bounce around at high velocity, typically stunning and then killing the player in a matter of seconds.

Both The Wall and Communications Array feature rooms where the rain is permanently non-lethal, as a transition between higher, safe rooms and lower, lethal rooms.

In the minute before the end of a cycle in areas where Rain occurs, the background darkens. At thirty seconds before the end of a cycle, vibrations of the oncoming Rain can be felt and heard. From here, the Rain will most commonly increase steadily in strength from a drizzle to a lethal downpour over 45 seconds, after the last pip.

There is also a chance for the Rain and associated vibrations to suddenly stop mid buildup, before becoming lethal. This lasts for roughly 10 seconds with increasing numbers of single heavy droplets marking the end of the intermission. After this the Rain immediately jumps to its full strength and most indoor rooms will begin flooding.

Cycles
Each cycle in Rain World has a random duration, visible in the bottom left corner surrounding the karma symbol. The "pips" each represent 30 seconds, and each cycle can last a maximum of 26 pips with an extra 20 seconds not shown in the timer (13 minutes and 20 seconds). The minimum cycle length depends on the selected difficulty - and   have a minimum cycle length of 13 pips (6 minutes and 40 seconds), while   has a higher minimum cycle length of 18 pips (9 minutes). Of all the Slugcats, the has the shortest minimum cycle length of just six pips (3 minutes). The cycle timer can be seen at any time by viewing the map, and it will flash up automatically once half the cycle is gone.

Tips

 * Bubble Weed can be used to prolong breath underwater while searching for shelter in flooded underground rooms.
 * Cycle time does not pass while passing through gates, unless the rain cycle has already started.