Yeah I didn't know about Ridley since the size of Ridley. I was just thinking of another iconic character from Samus. I know others mentioned Dark Samus but they seem like their moveset would be virtual clones of Samus unless they have her exclusively Zero Suit.
Birdo would be fun, I would just picture the Egg Projectiles now. The only thing I am thinking is that is Birdo more popular then other choices such as Toad, Fawful, Waluigi, Bowser Jr., Daisy, Rosalina. Not to say Birdo is popular with all the appearances outside of Mario Bros 2 she made. He was the main boss and needs so more love. Although it is highly unlikely he is a Rep. Paper Mario has been thrown around a lot as well, I don't know about him though he may just become another Dr. Mario. Dry Bowser would be interesting to see, although would he be a clone of Boswer is the real question as well as if he is a worthwhile rep.
I don't follow Mother, but I assume like Lucas Nienten has moves Ness does not have? If so I'd be content if Mother had 3 reps.