Kingler

Kingler is the strongest Pokemon with access to the combination of Swords Dance and Hyper Beam, possessing a dizzying base 130 Attack. This gives Kingler cataclysmic wallbreaking potential, outright OHKOing Chansey given the chance. It also has exclusive access to Crabhammer, which will nearly always land a critical hit, largely making up for its mediocre Special. Kingler isn't exactly slow relative to RBY OU either, being just above Cloyster and Victreebel. This means it isn't completely reliant on paralysis support and is very capable of mowing down teams without it. Overall, while an uncommon threat, Kingler is very capable of running over weakened teams if given a mere turn to set up. Even if it doesn't get a full sweep, the holes Kingler can tear in a team can be more than enough for its teammates to finish the job.

So why isn't Kingler often seen on the big stage, fighting tooth and nail with Kanto's finest? Kingler's sweeping prospects are swiftly put down by paralysis, and this weakness often forces it out, causing it to forfeit any Swords Dance boosts it may have gained beforehand. Kingler's special bulk is also a pressing issue, with even neutral hits like Alakazam's Psychic 2HKOing it. Furthermore, its weakness to Electric-type attacks makes Pokemon like Starmie a royal pain, often causing it to be KOed even at around 75%. These factors make it deceptively difficult to find an opening for Kingler to sweep, and it therefore requires an experienced player to be successful.