I feel like, if Magikarp was in Smash, it'd be made to appear as a joke character to an untrained player, but secretly have a lot of really good tools that would fly (splash?) over the heads of casual players, and possibly some competitive ones early in the game's lifespan too. A joke with an explosive punchline basically.
I could image it having moves that barely deal any knockback and only deal mediocre damage, but are so fast thanks to their lack of impact that they can pile up quickly and make Magikarp the best at racking up KO percents in the game, or having a slow run speed and low jump height but incredible air speed, making splashing the real secret to Magikarp success. Maybe even give it a Shine-esque move that doesn't deal much damage or have any special properties but is so fast and has such a large hitbox that it's one of the best offensive moves in the game.
insert either daddy derek or seven arts looney tunes joke here