Special Encounter

Special encounters, also called phenomena or pheno are a mechanic in the game.

Encountering Phenomena
Phenomena may only occur in the Unova region. There are at least 2 phenomena at any given time and last ~15 minutes. They may appear at a wide variety of locations and there are no reports for them (like televisions for swarms).

Different phenomena are distinguished in-game by audio and visual effects; in most cases, they are named for the visual effect shown on-screen when each phenomenon occurs.

There are four types of phenomena: rustling grass, dust clouds, rippling water and shadows.

A Pokémon that may appear in a phenomenon, has the location listed as 'Special' in its PokéDex entry. The only exception to this is Feebas, which has a different encountering mechanism.

Items
Pokémon that appear in phenomena may hold a Mysterious Gem or a fossil, native to Unova.