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Places the entry hazard Stealth Rock on the foe's side. Can be used only once before failing. This hazard deals damage to opposing Pokemon upon switching in. Foes lose 1/32, 1/16, 1/8, 1/4, or 1/2 of their maximum HP, rounded down, based on their weakness to the Rock-type; 0.25x, 0.5x, neutral, 2x, or 4x, respectively. Is removed from foe's side of the field when they use Rapid Spin, or when user's team uses Defog. Pokemon with the ability Wonder Guard are not immune. In a double or triple battle, this move will affect all of the foe's Pokemon. Pokemon protected by Magic Coat or the ability Magic Bounce are unaffected and instead use this move themselves.
Stealth Rock was arguably the most influential and important move in DPP, and its significance has not changed in the transition to BW. Pokemon who are 2x or 4x weak to Rock-type moves are stripped of 25% or 50% of their health, respectively. This had an enormous effect on powerful Pokemon such as Yanmega and Charizard, who are instantly crippled and left at 50% of their health just by switching in. This forced such Pokemon to fall well out of OU. Even Pokemon with a single weakness to Rock need to be wary of switching in; Rapid Spin support is almost required to keep these Pokemon alive.
Spikes is a Ground-type equivalent, but must be stacked to do equivalent damage, and cannot hit Pokemon immune to Ground-type attacks.
Toxic Spikes is a Poison-type equivalent, but inflicts the poison status rather than direct damage, and cannot hit Pokemon immune to Ground-type attacks, Steel-types, and are removed by grounded Poison-types upon entry.