Phenomena are a mechanic in the Generation Vcore seriesgames. Phenomena are a means of encountering wild Pokémon, and in some cases items. There are four types of phenomena: rustling grass, dust clouds, flying Pokémon's shadows, and rippling water. Some Pokémon can only be obtained via this method. Phenomena will only appear after the player has the first Badge.
A phenomenon can be randomly triggered whenever the player takes a step in an area. Only one may be active at a time. An active phenomenon will generally continue to exist if the player moves away from it so long as they stay in the same overall location or room. A phenomenon will vanish after it is encountered or if the player picks up a visible item, encounters a wild Pokemon, interacts with an NPC, or exits the area or room entirely; it will also vanish if an NPC steps on it. An active phenomenon is not saved when the game is saved.
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. The audio of a phenomenon reflects the distance between it and the player: if the player is close, the sound will be louder, and if the player is farther away (such as if the phenomenon is off-screen), the sound will be fainter but will also never stop.
Rustling grass is a phenomenon that only occurs in tall grass. Rustling grass allows the encounter of a wild Pokémon. Audino can be found in any patch of rustling grass. Various other Pokémon, such as the elemental monkeys in Pinwheel Forest and Lostlorn Forest, evolved forms of Pokémon found in non-rustling grass, or Pokémon that would otherwise be only available in the opposite version can be found in rustling grass, but are less common than Audino. Rustling grass does not occur in dark grass, but it does in long grass.
Shards can only be found in Relic Passage and Reversal Mountain, and all other items can be found everywhere else dust clouds appear in Unova.
In addition, the Pokémon are only found in certain locations.
Rippling water is a phenomenon that only occurs on water tiles. Rippling water allows the encounter of a wild Pokémon when Surfed on or fished in. While Basculin's Red-Striped form is found in Black and Black 2 and its Blue-Striped form found in White and White 2 under normal circumstances, the opposite form can be found in rippling water.