Rough Skin is an ability in the Pokémon games. Only three Pokémon have this ability; they are Carvanha, Sharpedo, and Druddigon.
Effect
If a Pokémon attacks a opponent with rough skin with a Physical attack, they will lose a little of their HP. This can make it very hard for certain types of Pokémon to knock out Carvanha or Sharpedo without fainting themselves in the process.