@Abes3 Daisy has a huge fanbase herself, and people have demanded she get into Smash just as long as people have wanted Waluigi.

So, blaming her and her fanbase is pointless. Besides. Daisy likely got into the roster for the same reason why Lucina was picked over Chrom in Smash 4. They could simply paste Peach's moveset onto Daisy, tweak it a bit, and boom, you have an echo fighter.

So, I doubt Daisy took away Waluigi's chances to be in the roster anyway. She was an easy to make echo fighter that fills a major request fans have had for years. That's why she made the roster.

With that said, if the Mario series did get a brand new character who is not a clone or echo fighter, I can see two who ruined Waluigi's chance.

-Captain Toad has been pushed in recent years by Nintendo, his game is being ported to the 3DS and Switch, and he has tons of potential for an intresting moveset, something that Sakurai loves in a character. Putting him in would also fulfill fan requests to make the Toad character playable in Smash. Factor in the fact that Toadette can also be added in as well as an alt costume, and he's one of my front runners for being a newcomer.

Paper Mario- While his stock has fallen in recent years due to games with a mixed reception, he has always been a popular pick. He has vast potential for a moveset, represents the RPG branch of the Mario franchise, and would be different enough from Mario to justify his inclusion. Even the argument that adding him would put three versions of Mario in the same game is no longer valid given Smash Ultimate has three versions of Link in the game already.

So, I think Waluigi's chances were taken down by two Mario characters who are more important then he is.

Which is the key problem here, Waluigi is not that important to the overall Mario franchise. If he's going to be a rep for the Spin-off games like Mario Kart and the Mario Sports games, then why should he get in over a Koopa Troopa or Shy Guy who also appear in those kinds of games? Speaking of which, Peach(and Daisy) already have the spin-off games covered in their movesets.

The only thing Waluigi has going for him is a rabid fanbase who appears to be willing to do anything, even crossing lines and hassling Sakurai to get him in.