Ambient entities

Ambient entities are objects that appear and move around in the background. They are also not interactive. They depend on the time of day, biome, and weather. Some are rare, and some are very common. Clouds can be considered background entities although they aren’t affected by biomes. Ambient entities' motion speeds up with time.

Rare clouds
Every time a cloud spawns, there is a chance it will instead be one of these rare clouds.

Trivia

 * The bats more accurately represent the bats from the Bat Scepter rather than the enemy bat