My 7 Newcomers
Echoes
Isabelle: Popular AC character
Kat & Ana: (Ice Climbers echo) surprisingly easy to echo. Swap hammers with... KatAnas, freezie(s) with shuriken(s) or Kunai(s), and blizzard attack with Sharp, or hard hitting Sakura petals. Up Special, Side Special and standard moveset stays the same Final Smash can be their old Assist Trophy special just enhanced to better KO enemies.
Blaze The Cat: (even though its most likely gonna be Shadow who I'm also fine with) A Fire focused moveset with speed, and acrobatic skill sounds fun to use
Lycanroc or Gardevoir A Geokinectic wolf or a graceful psychic/fairy type with the ability to use black holes either one.
Amaterasu: She has a variety of weapons that she holds on her back and uses telekinetically: A Celestial Brush (her tail) that can create objects and obstacles with her ink as well as cut and attack enemies with it, A Reflector that can counter and reflect attacks it can also quickly be used offensively as well as defensively making it the most balanced weapon she has other the her Celestial Brush.
Rosary Beads can be used as a whip and the beads can be fired as bullets promoting long range speedy attacks. Finally the Glaive (blade), a long but somewhat heavy blade releases powerful attacks that are somewhat slow promoting close range power attacks Sakurai could either mix the uses of Al weapons together, or input a stance mechanic to change between the four weapons and moveset but Special Moves and throws will stay the same. (Darn it! I always end up rambling when it comes to Amaterasu )
Sora: Cut skyscrapers to pieces with one slash, various elemental attacks, flight, different forms, healing, control gravity, stop time, need I go o-.
Shantae: Other than the Genie's iconic transformation abilities, she can shoot various fire attacks (fireball, triple fireballs, flamethrower) with could work like Robin's elethunder (without the limited tome mechanic), She can summon Pike balls to surround her and take enemy attacks as well as attack enemies, and she can summon a large storm cloud to smite enemy right in front of her.