Mass Outbreak

Mass outbreaks, also known as swarms are a feature in the game that allow the players to catch Pokémon that are usually rare or not native to the region. Swarms may appear anywhere and anytime (locations of swarms are not displayed in the PokeDex), but they seem to be related to the location (Petilil in grass, Wingull at sea etc.).

Swarms have four Pokémon on the designated location, walking around in the overworld, lasting ~30 minutes. Once the player goes to one of these Pokémon and interacts with them, a wild encounter of that Pokémon ensues.

Checking televisions (except Unova) allow the players to keep track of these outbreaks; active swarms are reported as breaking news displaying the location and the species.

After an encounter (either catching, fainting or fleeing from the Pokémon) the player cannot interact with the same Pokémon again in the active swarm, even if its overworld sprite is still there.