Sonic - Golden RingsYes, that seems obvious, but they're actually solid, sharp-edged arm guards. Surely if they were making them to refer to the rings they would have just... you know... used Sonic Rings...?
Golden LinkSo, it could be a reference to Darknut, or to the connection between Zelda and gold cartridges...
Frankly, both of these seem particularly stretch-worthy.
Green TrainerBrendan from Pokemon Emerald wears a predominantly red and black top. His bag and headband is green and his hair is white.
Pokemon Trainer's costume is orange and grey with a green bag and hat and red hair. Some similarities, sure, but no more than, say, Pokemon Gold/Silver Trainer (which is my favoured explanation so far).
There's more to this than we're saying. There's something in the red hair - the other Trainer costumes have black hair (except Sepia Trainer), so there's something in that.
FalconThe image doesn't work. And no, SSB64 Captain Falcon looks like Captain Falcon. And going back... it looks like Captain Falcon has the pale blue alt. colour in SSB64 as well (as one of his team colours).
Foreman Spike outfitNot really... it's dark brown with brown shoes and a green hat, which is nothing like Mario's black and white with blue shoes outfit.
Wario - Booster OutfitWhy would I dismiss this for being SMRPG? It was released in America, and the similarities between Wario and Booster are recognised worldwide! I think this is one of the BEST suggestions! I shall check into it.
Pokemon Trainer - Alt EvosI kinda like this explanation, even though I struggle to see it myself. I'll add it in anyway - and thanks for explaining the female trainer reference as well!
LucarioAhh of course! Why didn't I check that when I was going through shinies at serebii.net
Jigglypuff - Red FlowerHmm... Nyaaaaaaaaaah!
Ice KirbyYou just posted sprites... he's white! Not blue!
Dark LinkThat's right... Dark Link. Bwahaha. No seriously... don't get too hung up on the minutiae of the series storylines and minor distinctions. I'm going to hazard a guess that Dark Link and Shadow Link are referred by the same name in Japan.
(Later...) Oh, to quote Sakurai from that link The Qu posted:
Ahem
WarioWare - Original Costume ColoursErr... I added that one already
Nana's red costumeThat's a really bad screenshot. Nana's pink in the game. Trust me. I gots da sprites. OK, she's red on the AMERICAN boxart... I'd say it's possible thanks to the NES Classics being popular in Japan... but wasn't this also an alt in SSBM?
Of course, Ice Climbers might have been so desperate that they had to use strange sources. Still... there are probably better ideas.
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A final note, aimed vaguely at Flip's comments at the top of this page, but relevant to everyone.
Just because you see something and immediately think "Oh, that must be a reference to x" is no reason to just flat out assume that's the case.
I want this to be an interesting and, above all, accurate listing. Speculation is one thing, but actually using your brain and the resources available is another. For example, everyone loves suggesting Fox's costumes are from Adventures/Assault/Command. Why is this? His costume doesn't change between any of these games. Everyone just jumps to a conclusion, or references something someone else has said. The rumour spreads and we all suffer. I've made this mistake several times on NinDB before now, and I don't want to go telling unsubstantiated rumour as fact, as these things spread and become common (but wrong) knowledge.
I'll take Falco as another example. Yes, I was convinced his red costume was from Assault, just like most of you. Until I checked it out, and sure enough he also has this alt. in SSBM, which means it's not from Assault (if anything, Assault nicked it from Smash!) So always worth covering your bases.
We may never be able to prove some of the more obscure ones, but we can err on the side of caution and use an "unsolved" tag or similar. Just don't state things as fact unless you've checked them. Make suggestions, but don't be offended if I am not convinced. Don't argue the same point - find a new angle. Find more images.
And remember - they're not all going to be cameos.