Hidden Grotto

Hidden Grotto is a feature in Pokémon Black 2 and White 2 that allows the player to find Pokémon with Hidden Abilities or items. The contents of the Hidden Grottoes are random, and if they are empty, for each 256 steps, they generally have a 5% chance to regenerate, usually with different content than what was inside on the previous visit; however, the chance can be increased (to 15%, 25%, 35%, or 55%) with the various levels of Grotto Pass Power. Hidden Grottoes will not regenerate unless the items are obtained or the Pokémon are caught or defeated by the player.