That gives me an idea for a Fun Forum Game™. Make a fighters pass of characters, and the only rule is that they must have an echo accompanying them. Uniqueness can very.
Fp6: Spring Man (ε: Min Min). They do the belmont thing: Spring Man has a few kicks in his moveset.
Fp7: Phoenix Wright (ε: Miles Edgeworth). As Edgeworth is a prosecutor, his playstyle is more of a rushdown, as compared to Phoenix's more calculated, read-based one.
Fp8: Bravely Default 2 Protagonist (ε: Agnes). Once again, all cosmetics.
Fp9: Tails (ε: Eggman). This sounds ridiculous on paper, but here me out: They're in SA2 style mechs, hence the ability to echo eachother. They're Ryu/Ken levels of different.
Fp10: Alolan Marowak (ε: Marowak). I was desprately searching for some pairing of Pokemon that could work, but the easiest option was staring me in the face. Marowak is the Lucina to Alolawak's Marth, but hopefully better balanced.
Fp11: Maxwell (ε: Lily). Once again, all cosmetics.
Challenger Pack 6: Spring Man, who comes with Springtron. They have their canon differences, meaning that while the moveset is functionally identical, Springtron, who doesn't have the comeback mechanic and moves slower, can buff himself to move faster and have instantly charged Smash attacks. Springtron is also heavier.
Challenger Pack 7: Frisk, who comes with Chara. Chara is about as similar to Frisk as Daisy is to Peach: there's nary a mechanical difference, it's just vanity animations, but Chara is a lot more... shall we say, lively, than Frisk.
Challenger Pack 8: Arle Nadja, who comes with Amitie. Amitie is actually a very different Echo, being basically a Ken level difference here. She has alternate takes on some of Arle's attacks, and has a different partner character coming alongside her (Donguri Gaeru instead of Carbuncle). Amitie would be lighter.
Challenger Pack 9: Crash Bandicoot, who comes with Coco Bandicoot (Fake Crash is too similar). Besides some slight hurtbox differences, and totally new vanity animations, not a whole lot changes between the two. Maybe Crash is slightly faster while Coco has slightly better frame data. Coco would be lighter.
Challenger Pack 10: Gonna cheat a bit here and say Dixie Kong, who comes with Donkey Kong Jr. echoing his dad/son/himself but older. Relative to DK, the moveset is identical but it's on a character who's faster and has a smaller hurtbox, so it's a fair bit weaker. DK Jr. isn't a superheavy like his old man/boy/future self, but he is a very heavy cruiserweight.
Challenger Pack 11: Cheating again with Waluigi, who comes with Shadow Mario as an echo of Mario. Shadow Mario can apply ink like the Inklings, and his Final Smash is Mecha-Bowser instead of Mario Finale, but otherwise it's the same basic deal. (Hey, if Chrom can double as an FS and an Echo, so can Shadow Mario.).
If 10 and 11 have to have the Echoes be for the newcomers themselves, then 10 will be Isaac with Felix (IDK how different they'd be, but to sate the fans I'll say they're at least Ken-lite), and 11 will be... Bill Rizer and Lance Bean are so similar you could make them alts, and they're third party... uh, Toad with Toadette, and they're functionally identical, I guess.
Three third parties, three first parties, even steven. Would've liked to do Pokémon, but I'm not resorting to putting in the same species twice. This was actually really hard, to the extent I had to resort to technically doing it but not doing it in the spirit of it.