A Dusk Ball is a Poké Ball that has a 3.5× catch rate in dark places. It can be obtained by crafting it, buying from a shopkeeper, or as a tier 1 special drop.
If it is currently dusk or night, the Dusk Ball will have its increased catch rate. Otherwise, the location of the Pokémon to be caught must meet the following requirements for the Dusk Ball to have a 3.5× catch rate:
The Pokémon must be located at a height level of 64 or lower.
The Pokémon must be in a place with a light level of 14 or lower (i.e. not in direct sunlight).
Rain in an area of direct sunlight will not trigger the Dusk Ball’s effects.
Snow in an area of direct sunlight will trigger the Dusk Ball’s effects.