Off the top of my head that I can think of, these are characters that have basically no representation in tournaments:
Bowser, Link, Zelda, Toon Link,Samus, Marth, Ike, Robin, Kirby, Falco, Jigglypuff, Doc, and Mii Gunner.
Everyone else I think has at least one noteworthy player. Of course, a bunch of those characters I listed probably have some representation...but I don't know of them. Again, off the top of my head.
Bowser has Ash23 if you're a VGBC watcher along with Oco Le Troof and Exist while Kato, Scourge, and Big Sean for Cali's scene, Zelda has Nairo whenever Nairo wants to use her, Toon Link people already said, but they're not people know if Toon Link's mentioned, Ike would have had known players had Apex not been I guess, unfavorable is the word, to the Ike players, Ryuga, Ryo, San, and Blitz, Robin has Trela?, Kirby has Mike Kirby - come on, man, it's in his name!
-, and Dr. Mario has Rice if you're familiar with the Cali scene. Of all those names, only Nairo, Trela, Mike Kirby, and maybe Rice are well-known names. Everyone else depends on whether or not you follow/live in the scene or you're part of that character's community and follow everything that's going on.
So, that leaves Link, Falco, Jiggles, and Mii Gunner. I think Link has Izaw for a notable player who's done amazing things with Link, but that's pretty much it from what I know, Falco doesn't have a notable main player, but he has notable secondary players like GimR, I'm not sure on Jiggles and Mii Gunner.