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This is Zangoose.
In gen 3 Zangoose was a really good in-game mon. It learned Swords Dance and STAB Quick Attack really early. You could catch it before the 4th gym and it was stronger than most late-game mons for the rest of the game. It also was a decent competitive mon. 115 base attack, 90 base speed, Swords Dance, Shadow Ball and strong STAB moves / priority made for a good sweeper. Not the best, but good nonetheless. It was UUBL, just like Alazakam, Arcanine, Breelom and Dragonite.
Fast forward to gen 6/7. Zangoose is stronger than ever. It was progressively buffed in all generations. It learned Close Combat in gen 4, got Toxic Boost as a hidden ability in gen 5 and benefited heavily from the Knock Off buff in gen 6. Now it's still a good in-game mon, as some people who played ORAS already know. And how would a mon with 115 base attack (multiplied by 1,5 because of Toxic Boost) and a 210BP attack on Facade, good coverage on Close Combat / Knock Off and STAB priority do on competitive?
Untiered. Fucking Untiered. An offensive monster. Why? Because it's a vestige from an era when GF still cared about balance. Being an offensive mon with decent speed and mediocre defences doesn't cut it anymore. If you want to be a sweeper in gen 7 you need to be a glass cannon with ridiculously minmaxed stats (i.e. Kartana and Mega-Beedrill) or have mad utility other than your sweeping capabilities. You haven't any of those? Don't worry, maybe GF will give you an overpowered gimmick. They don't give exclusive megas and Z-moves anymore, so it needs to be a broken ability or Gigantamax. Having a broken ability worked for most OU mons in the current gen, including Greninja and Mimikyu. Oh wait, those two are shillmons. Nevermind