Sand Stream is a special ability found in certain Pokémon, primarily those of the Ground type. When a Pokémon with Sand Stream enters battle, it creates a sandstorm that lasts for five turns. This sandstorm affects all Pokémon on the field, dealing damage to those that are not Rock, Ground, or Steel types at the end of each turn. Additionally, during a sandstorm, the Special Defense of Rock type Pokémon increases by 50%. This ability can be strategically used to enhance the defensive capabilities of a team while also causing damage to opponents, making it a valuable asset in battles.