Kirby can easily win a national. All the player needs is the ability to host the tournament himself and post the rule "In the event of Kirbycide, Kirby is declared the winner." However, it doesn't say the game has to END in Kirbycide for Kirby to be declared the winner.
Sure, the host may not win, but after he shows off the strategy, plenty of players will promptly drop whatever character they are playing and start using Kirby. Soon, other hosts and TOs will try to abuse this rule at their own tournaments. However, by then, everyone will know. Hordes of freshly converted Kirby mains will show up, each one thinking they are one of the only few who know the secret of the ruleset.
But they were wrong.
By the end, not only has Kirby taken first place, every character in the top 8 is Kirby. The tier list is reconstructed from the ground up. Spacies drop to mid tier because it only takes one mistake to lose the entire match. Kirby takes the number 1 spot. Eventually, the metagame evolves into both players camping the edges, holding B, and yelling every obscene word they know at their opponent in hope they'll get angry and hit them in real life, thus disqualifying them.
Melee slowly begins to die out. Player after player moves over to Brawl, P:M, Streetfighter, and even Dora the Explorer PC games. ANYTHING to escape the disaster that is the Melee metagame. That is, UNTIL... out of nowhere comes Hungrybox, fighting off Kirby after Kirby with well spaced Bairs and 5000000001 jumps. He outranges their options. He cannot be Kirbycided. He becomes unstoppable. Soon, everyone realized that Puff is the answer to the Kirby pandemic. Just as with Kirby before, player after player converts to Puff, ushering in a new age of Melee.
With the Kirby infestation finally over and done with, Melee dies anyway because the only matchup is Puff dittos.
So now... you know. THIS is why they put Kirby last on the tier list. THIS is why most rulesets don't specifically mention Kirbycide (after all, they can't allow anything to spark this idea). THIS is why Puff was number 3 on the tier list last year. Someone or someTHING doesn't want Kirby's secret to get out. But we know. And we can never un-know. And that is why they will not stop hunting us. Not until every one of us lies cold and dead. That's why I'm where I am. Hidden in the desert where no one can find me. I'll be safe here.
Wait... what's that? I...I hear something.
Yes... something is definitely approaching. I think it's them...
Please... hear me out one last time...
If... if I don't make it out alive... Tell my wife... tell her.... AAAAAAAAAAAAAAAAAHHH! NO! NO! GET AWAY! GET AWAY! STOP! STOOOOOOO-
