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I hit a nice peak using a swagplay team. I can't tell you how many times I've been in a completely lost game before I land a swagger on a sweeper, and proceed to faceroll an entire offensive team through confusion hax. It's a very solid matchup against most all offensive teams.
When you use a partial swagplay team vs Stall, it forces swagplay counters like chansey and rotom-w to come in, and that gives a free setup to dangerous stuff like mega-mawile and lucario. What makes swagplay useful against even stall teams, is that when theyre sitting there confused and hoping to pp stall you out or something, they only have a 50% chance to react on whatever your switchin is. A well built swagger team is NOT deadweight against stall, it can force switches, and if they want to stay in then their current pokemon has to endure a coinflip every time it wants to move.
imo the two best swagger pokemon are definitely klefki and thundurus-i, and they have ways of getting around commonly listed swagplay counters.
Klefki has access to toxic orb Switcheroo, which completely wrecks rotom-w, magic bounce, and chansey switchins. It doesn't matter if aromatherapy or natural cure cures the poison, the toxic orb makes it so that the status effect always comes back, and ensures they cannot stay in to handle the swag. Klefki also has an excellent defensive typing, and has decent defensive stats that make it stand apart from the rest of the frail prankster pokemon.
Thundurus-i is unlike most other prankster pokemon because it actually has a solid offensive presence. pokemon like gliscor and xatu get lured into thundurus to take a swagger, and then get destroyed by an offensive set like tbolt/hp ice/sub/swag. With access to knock off and toxic as well, its very difficult to find a defensive switchin when every offensive switch gets swaggered.
It is not as simple as slapping one swagplay counter onto a team and having that deal with the whole issue. If your counter gets eliminated from a surprise set like that ^ theres really nothing you can do except pray you hit through the swag throughout the rest of the match. The odds of the opponent breaking through swagger are absolutely terrible as well, its not as simple as winning one 50-50 and taking out the swag user. You have to win MULTIPLE 50-50s in a row, because that swag player is definitely going to be using sub on every turn. Confusion itself is just amazing in the current meta as well. Swagger klefki/thundurus practically soft-counter aegislash because of his sword/shield mechanics, makes mega-pinsir afraid to ever mega-evo, and turn every non-scarf physical sweeper into a threat to their own team once ditto comes in.
idk how i feel about swagplay getting banned, but it is not as simple to counter as some people are making it out to be in this thread. The only times I ever felt like I had an unwinnable matchup were against something like a mega-venu/chansey/gliscor team, and even then i still had some counterplay available. Also to people suggesting stuff like numel and safeguard, im sorry but a good swagplay team is going to have other threats that will walk all over you if you try and pull gimmicks like that lol