It seems like most of the characters I presume did well on the ballot, but aren’t fighters got a little something special in Ultimate. 3rd party characters either got assist trophies like Shovel Knight and Bomberman or spirits like Rayman, Shantae and Geno. Shadow’s assist trophy also returned with a bit more flare than in previous games.
As for the Nintendo characters Waluigi, Skull Kid and Isaac had their assist trophies return and received new Mii Fighter costumes/hats (Dixie Kong also received a hat). Isaac’s assist trophy was enhanced compared to the one in Brawl and the Moon was also made into an assist trophy which is intrinsically tied to Skull Kid. Krystal also got an assist trophy, and Toad was featured more prominently in Peach’s moveset.
The only notable characters who didn’t get anything special was Bandana Waddle Dee and Paper Mario who only got spirits, and since they are owned by Nintendo it’s not as notable as Geno or Shantae getting one. At least for Paper Mario him not getting a costume makes sense, meanwhile they easily could have made BWD’s bandana a hat or did what Streetpass did. Also there is at least a Paper Mario stage which returned from the 3DS version, meanwhile there aren’t any modern Kirby stages, not to mention they neglected to give Bandana Waddle Dee a trophy in the previous games… man my boy deserves better.