In reference to the title,
Does Isai even get paid to play this game? And if so, is it more than "everyone throw 10 bucks in the pot at our smashfest" money?
Anyway, back on topic. Hello Jakecor. To teach that pesky mario a lesson what you want to do is when he throws you off, use your double jump to position yourself above and away from the ledge. You don't want to be too close because then he can knock you right back out again.
When you use your up+b, aim it so that when you come back, ness will skim the top of the level starting from the ledge on back. This will shock the living bejesus out of him if he is standing on the ledge. You also don't want to be too far away because ness loses his shocking ability after traveling a certain distance with his up+b. Just experiment with it. You'll get it.
I like to aim for the top corner of ness's ridiculously oversized head if i am coming back from above (which is usually the best approach because if something goes horribly wrong like a stray fireball you might get another chance to up+b again).
This may take a bit of practice at the beginning, but after a few times you will get the hang of it. You will also find that your mario friend might want to be a complete ***** and lob fireballs at you. If this is the case and he ends up hitting you, your up b will obviously fail. Fear not, young padawan, for there is a solution. Simply keep spamming up b and aim DIRECLY for mario no matter where you are. He may be an iconic fireball throwing italian plumber, but he has probably underestimated your biggest asset: you can turn yourself into a god d*mn mother f*cking human bolt of lightning.
He will be a little more leery about being an annoying ledgeguarder after you punish him for his insolence.
