Awesome quiz! I would also include Alph (alternate for olimar in smash 4), accept mii brawler (that is his real name), and separate Samus/Zero suit samus and Zelda/sheik. Not trying to discourage you or say your quiz is bad (it's actually fantastic) I'm just trying to help you make it even better. Awesome quiz!
This quiz is thorough but a bit excessive and doesn't properly separate some characters. Costumes shouldn't be considered as different characters imo but echo fighters should still be separated. Also I'm super confused as to why you put Samus and Zero Suit Samus as the same character when they are completely different in all Super Smash Bros games. By that logic, Link, Young Link and Toon Link should all be the same character as well, but overall I would advise against doing this and just create a list that mimics the current roster of SSBU. Also, mii fighter should be corrected to mii brawler and if you're going to include charizard as a character, you should probably remove pokemon trainer and add squirtle and ivysaur. Overall a nice quiz but it still needs a few fixes.
Byleth (Fire Emblem)
Min Min (Arms)
Steve (Minecraft)
Sephiroth (Final Fantasy)
Pyra/Mythra (Xenoblade)
and also remove Charizard because now he is with Pokemon Trainer