Pokemon battles are dangerous things, especially in the era before modern medicine. Today, serious injuries are kept to a minimum and deaths are extraordinarily rare, but the very term "pokemon battle" belies its origins as a blood sport. Some of these pokemon accepted their deaths as the inevitable result of facing a much stronger opponent or learned to hate the very concept of battles. But whenever a pokemon goes to the grave believing it would have lived if not for a particular weakness, a Sableye is born.
Sableye are a difficult pokemon to fight against, for not only is there no way to gain a type advantage on them, but their strange, impish form does not offer a single weak spot. Sableye make the first move of every match, because even the fastest pokemon instinctively look for either an opening or an elemental weakness before attacking, yet neither can be found on a Sableye. Therefore, the baffled, indecisive opposing pokemon inevitably freezes in place until either a Sableye's attack or its trainer's tactics begin the match, at which point their retaliatory mechanism takes over.
Once the fight actually starts, however, Sableye lose far more matches than they win. They have devoted their dying wish and their training alike to minimizing weaknesses, but in seeking to cover every weakness, they have forgotten the importance of strength. Although they are not weak against any attack, neither can they shrug them all off; they are merely damaged equally, unlike victorious pokemon and trainers who understand that they can not possibly cover every weakness, merely maximize their own skill and hope for favorable match-ups. Yet Sableye are still prized by trainers, not because they lack weaknesses, but because for an expert tactician, making the first move is the difference between victory and defeat.