Heres my 24 personal choices to finish up the roster plus stages & assists, was running out of items & bosses (some assist i listed could also fit this role, maybe even like Rathalos). Like I said it was fun to get a little crazier with ip that have little chance of actually being in Smash.
In no specific order
1 James Bond (Oddjob, Dam)
2 Banjo & Kazooie (Gruntilda, Gruntys Furnace Fun)
3 Commander Shephard (Tali, Normany Galaxy Map)
4 AGES - similar to allstars racing, defaults as Segata but morphs into iconic sega characters for specific attacks including Beat, Akira, Ryo, & BD Joe (Aiai, Daytona USA)
5 Yoshimitsu (Devil Jin, Astral Chaos)
6 Spiderman (Venom, Daily Bugle)
7 Batman (Joker, Arkham Asylum)
8 CJ (Big Smoke, Grove Street)
9 Bart Simpson (Homer, Treehouse of Horror)
10 Goku (Frieza, Namek)
11 Kos Mos (Elma, Cloud Sea of Alrest)
12 George (Eustace DeMonic, Moon - Lunar Tech)
13 Wesker (Mr. X, Salazar Castle)
14 Star Killer (Storm Trooper, Death Star)
15 Lu Bu (Natora Li, Base Siege)
16 Monika (Sayori, Poem Notebook)
17 Farmer (Harvest Goddess, Mineral Town)
18 Rachel (Sturm, Cosmo Land)
19 Mai (Athena, KoF Stadium)
20 Chell (Glados, Aperature Labs)
21 Yugi (Kaiba, Shadow Realm)
22 AVGN (Guitar Guy, Nerd Room)
23 Leonardo (Shredder, Channel 6)
24 Crypto (General Armquist, Furon Mothership)
HM - idk maybe they could have gotten a stage, item, or assist: Paperboy, Frogger, Earthworm Jim, Adventurer (Atari), ET