>>50536964There's been 4 separate Fairy/Steel mons who've fucked the meta in the ass.
Klefki's Swagplay broke the game so hard that Smogon needed to ban Swagger and Gamefreak needed to nerf confusion in the next generation.
Mega Mawile was the dominant Mega in the meta until the CHALK core was discovered and has the 2nd highest effective attacking stat in the history of Pokemon, the equivalent of 268 base Attack.
Magearna was a dominant force in Smogon for all of gen 7 and then got buffed in gen 8, giving it no counters in OU and making it the spiritual successor to Mega Lucario, inspiring pic related.
Zacian is the reason I had to say Mega Mawile only had the 2nd highest effective attacking stat, since it has the equivalent of 282 base Attack. Plus a base Speed of 148, outspeeding the entire legal metagame outside of Regieleki, Ninjask, Electrode, Pheromosa, and Calyrex-S.
Interestingly, none of these mons were broken specifically because of their typing. GF just seems to really like giving overpowered shit to Steel/Fairy types.