And by Swagplay, I mean this. While this is clearly a worst case scenario, it still epitomizes how much luck can influence a Pokémon battle. Swagplay is arguably the best way to turn a game into a game of pure luck, and it's currently being looked at by Smogon, with several possible outcomes, but the only two that are likely at this point are either a combo ban or nothing. While Swagger is pretty much never used outside of this little trick, banning it altogether still seems excessive. Banning individual Pokémon would also be a very stupid move, especially since the likes of Klefki and Sableye can run other sets and still be very effective. These two notions are agreed upon by just about everybody, so that's not happening.
There are still a few questions worth asking, though. If Pokémon can (and usually will) get banned according to their best set, and this is the best set the likes of Klefki have to offer, what's so different in this case that the ban needs to go elsewhere than the species? The obvious answer is that unlike the top sets for Pokémon like Blaziken, Kangaskhan or Genesect, this requires no skill to use, just some luck. However, is that enough to justify combo-banning Swagger with either Prankster or Foul Play (or maybe even both)? Also, if no one has problems with the very luck-based paraflinch, then what's so different about this? Is it even as effective as paraflinch? Questions like that are worth pondering, and show that nothing can be black or white in such a complicated game.
I've always personally been in favor of keeping an element of luck in the game, as long as it doesn't become the big focus. Have we reached that point with Swagplay? You can win a lot by using it, and you can also lose a lot, but the damage you do with it (or lack thereof) is not dictated by skill at all, which is an issue. Let's just say I have less of a problem with a game being turned around with a lucky Fire Blast miss than this, because the former isn't really intentional (not to mention, that's the price of using Fire Blast compared to Flamethrower), and being the beneficiary of such luck happens a lot less often.