It's not uncommon to find playthroughs where a player decides to go through an entire game of Pokemon with something silly, like Bidoof. But Magikarp, a fish Pokemon that's largely taken as the most useless Pokemon ever? That's a whole other level of insanity. Still, it can be done.
This (sometimes sped-up) video shows Meikachuchu going through most gym leaders and the entire Elite Four on either Pokemon Fire Red or Pokemon Leaf Green—all with a singular Magikarp. The Elite Four are basically the closest Pokemon has to final bosses.
Some matches here aren't so bad; Magikarp is leveled such that it can tank through some threats. But there are some moments in here where you think, wow, that battle looks painful and tedious—is playing through with just one Magikarp worth it?
But then you get to the end, and this happens:
And you're just like yes. Yes it was.
Naturally this undertaking required a lot of items, but even so, there were a lot of close, nerve-wracking moments. Like having to use struggle to go up against a ghost-type, because Magikarp, in all of its complete usefulness, only has three moves: splash, tackle and flail. All normal types, which don't affect ghosts! Thankfully, the move struggle has no typing, but having to resort to it is still ridic.
So, kudos, Meikachuchu. Your Magikarp run-through is amazing.
Pokemon: Magikarp Edition [Meikachuchu]