Power ups can be a gameplay mechanic kind of like how hyrule warriors had the items from legend of zelda games. Anyway here's my roster ideas.
Mario: cappy
Luigi: poltergust
Peach: parasol, hearts, and emotions
Daisy: flower/crystal power
Rosalina: wand and lumas
Pauline: mini toys and music
Captain Toad: pick axe, turnips, and spores
Toadette: pick axe, acorns(works like toad's turnips), and super crown
Toadsworth: cane and toadsworth twist
Yoshi: eggs, tongue, and wings
Birdo: shoots eggs, bombs, and fireballs
Queen Bee: honey bucket, honey combs, and stinger
Sprixie princess: hammer and wrench bells they all used to create the rocket from 3D world
Donkey Kong: punches, headbutts, grabs, and barrels
Diddy Kong: tail and peanut popgun
Dixie Kong: ponytail and gumball popgun
Funky Kong: surf board and barrel blast
Geno: arm gun
Mallow: weather attacks
Piantissimo: fruit/pepper toss and dashing
E. Gadd: super poltergust 3001
Nabbit: sack
Princess shokora: attacking in her cursed forms
Wario: motorcycle, farting, and warioman
Waluigi: dancing and tennis
Ashley: red
Bowser: fire breath, clawing, and tail smack
Bowser jr: clown car
Kamek: wand
King Boo: dark moon jeweled crown
Petey piranha: cages
King K. Rool: blunderbuss kannonballs and belly
Fawful: vacuum headgear and fawful blaster
Vivian: teleportation and her fire attacks
Shadow queen: shadow hands and dark energy
Count bleck: scepter and chaos heart