This is the ultimate discussion. Who would win between a Metapod who only knows Harden, and a Magikarp who only knows Splash?
Well, I believe it would be Metapod, and here's why. Since Harden has a PP of 30, and Splash has a PP of 40, Metapod would be able to use Struggle first. Since Metapod has more HP base stats than Magikarp, Metapod should be able to kill Magikarp before Metapod kills itself from the recoil. Even if Magikarp would be able to waste the 10 remaining Splash attacks after Metapod is able to use Struggle, Metapod would not be much affected since it has used maximum Harden.
Of course, this would all depend on which Individual Values each of the two Pokémon have, but on an average, I'd say Metapod wins.
This is only my point of view, and some of you might disagree with me. What do you guys think the outcome would end to? I'm eager for an answer.
(It would have been helpful if someone would make a recreation of this on a real Pokémon game)