I know I'm quite late to this "argument", but I really feel like some of these points are very flawed.
Lucas was in Mother 3, released four years after Dinosaur Planet. He was also only the second Mother representative.
Ike was in Radiant Dawn, which is a Wii game. His series only had two characters and one was cut in Brawl.
Both are main characters, which Krystal is not.
Won't even touch on Dedede.
What was your point again?
Being a protagonist does not necessarily mean you are unique. Inversely, not being the main character doesn't mean you aren't unique. Kuma asked about uniqueness, not about "statistics". Plus how many playable characters in a series there already are has absolutely nothing to do with uniqueness. Are you saying if characters like Toad, Ghirahim, or Zoroark got into Smash 4, they wouldn't be unique because their series already has major representation?
I'll indulge your weak argument because it doesn't even work regardless. Ike is a slow, heavy sword user, which is different from Marth and Link uses projectiles, along with other gadgets. Lucas relies on his PK abilities more than Ness does, and has some little changes in his moveset to make him interesting. This actually works because there are only two of them, Ninten would be as ridiculous as Krystal. King Dedede... okay, okay, let me hold back the laughter... he summons minions, has a huge hammer, has a unique recovery... pfft, I know right, he's such a Kirby clone. Plays completely differently to any other character in the game.
This doesn't really answer why they were unique enough to warrant being playable, it just describes how "uniquely" they played once they were already in the game. Also it proves that every character in Smash would play different from eachother and uniquely, including Krystal, especially if you view character movesets such as Lucas "unique".
Krystal is at best a lightweight staff user, though she never uses the staff. At worst she's another Fox clone who has the differentiation of being the 'lightest' when Fox and Falco are already quite light already. Very, very boring.
If she was a semi-clone of Fox, I would agree that would be fairly boring, although judging by what you consider unique, she would still apply. I do wonder how you could consider a character that would use a staff (a weapon not yet in Smash) as something "boring". If it's just by your personal opinions, then it would be very subjective. Even if you ask somebody (somebody logical) that does not support Krystal if a moveset using her multi-functioning staff would be boring or not-unique, I doubt they would think either.
...You what?
You mean to tell me you were okay with waiting 5 years for a Sequel to a Starfox game, and when it came: you got Starfox Adventures???
You realized Starfox Adventures is why Starfox died right?
It took several years past Starfox Assault came out for me to actually try/enjoy it because I didn't trust the team anymore after Starfox Adventures.
I in fact remember being a kid, Christmas Day. I got a Gamecube. Super amazing graphics in my eyes. The game it came with? Starfox Adventures. 2 Days in I gave up, heart sank, and would have to wait for SSBM to enjoy that machine.
Starfox Adventures is a good game. It got good reviews, it sold well, it was well received. Like what was said before, alot of purists denounced the game because it was a departure from the previous two titles. Changing the style and genre of a game does not make it bad. Bad gameplay, bad controls, bad graphics (to a lesser extent), bad narrative, etc. make a bad game. Granted, none of these factors in Adventures were the same as previous Starfox games, but they were all decent to good, and none of them were downright "bad".
Also, as popular of an opinion as it might be, Adventures was not the reason Starfox "died", no more than Zelda II caused Zelda to die or the Prime series caused Metroid to die. The main reason Starfox "died" was the back-to-back hit of less-than-stellar Starfox games (Assault and Command), both of which were closer to original Starfox and Starfox 64 design, and both of which were, believe it or not, much less favored than Adventures among the majority. Adventures did not even cause Assault to be received poorly commercially, as it still sold over a million copies, only a little less than Adventures. Plus if Adventures had really killed off Starfox, there wouldn't have been two games developed after it was released.
By your logic, even if Assault and Command had been flawless games, Adventures would still have caused the Starfox series to die, which is incredulously untrue.
What is relevant is: We have THREE Starfox characters. 2 of them are the Luigifications of each other. What you're arguing for is a 4th character of a game that basically died because of the character you're asking for.
And the reason you think she's unique: She has a stick. A staff. You're trying to make an even lighter form of Fox, but she be mid range and have a stick.
I just want you to think about this for a second: Krystal could be the reason a really unique character of a newer or less represented series doesn't get in.
Firstly, Krystal did not kill off Adventures or the Starfox series. The main protagonists are the characters that sell or do not sell a game, not the supporting ones. Tingle didn't kill off Zelda, Waluigi hasn't killed off Mario spin-offs. What caused Starfox to "die" was the mediocre to poor games, not a supporting character in them. Sure, she has a hatebase, but not one so large it would effect the sales, and more importantly reviews, of a Starfox game.
Secondly, since when is having a staff not cause for being unique? It would totally differentiate her and her moveset from any other character, and if implemented would guarantee her not being a clone. How would a character with a totally different moveset, and an exclusive weapon not be unique? There are unique characters that have a whole lot more in common weapon-wise.