Pokémon Sun and Pokémon Moon have been out for ten days already and aside from being Nintendo's most preordered game of all time as well as GameStop's most preordered game of the past five years, the bar has already been set high for challenge runs.
Nakano, a Japanese gamer who has been playing the game since release, beat the game with a single Pokémon as seen on his Twitter page. Not a legendary, not a starter, not even a Rattata. A fish. A fat, floppy fish.
Yes, Nakano beat the entirety of the seventh generation Pokémon titles using only a Magikarp that only had one move, Flail. And yes, this does mean the Magikarp couldn't even use Z-Splash to boost its attack. Nakano doesn't specify which version he beat, but the fact remains that he did it!
Nakano used a few strategies, with the most interesting and elegant being explained by Rocket News 24 who translated the Twitter page. He would stock up on healing items, then keep healing his Magikarp until the enemy ran out of PP. The enemy would then struggle, which hurts itself as well as the player, until it eventually fainted. Yes, Nakano literally let his enemies beat themselves to death.
How he dealt with Ghost-type enemies that he had to fight was to have have his Magikarp struggle against them, which hits any type of Pokémon. Other than that, the only move Yashoku (the Magikarp) had is Flail, which does more damage the lower her HP is.
On Nakano's Twitter page, you can see the stats, moves and other proof of completion in Japanese. Quite impressive, to say the least. Your move now, Pokémon Sun and Moon players! Time to come up with an even more insane challenge!