Blood Brother...
Each of the characters in SSBM has alternate costume color schemes to choose from. There's a rather neat detail for Captain Falcon's red uniform though... He's not actually Captain Falcon anymore, but dresses instead like the Blood Falcon, his rival racing clone from F-Zero. He even has the mark of his machine on the back of his uniform, complete with his racing number 25. (Captain Falcon's machine is the Blue Falcon, racing number 7)

Barrel Blast
If you turn all the individual items off in VS mode but still leave the frequency, barrels, crates & capsules will still fall from the sky. Of course they won't have items in them, and will often explode if you hit them.
Submitted by HexicDASH!

Tie Time
Donkey Kong would be completely naked if it weren't for his coat of thick fur (thank god). The only piece of clothing he wears is a necktie. If you look closely, you can actually see his necktie flapping in the breeze on some stages, including F-Zero's Big Blue.

Sword & Sheath...
Just a small detail about Roy's character. When you earn one of his trophies, you can clearly see that he's wearing a sheath for his sword... But during gameplay, there's no sheath to be found. Odd.

Pokédeath
This one involves the rather active Pokéfloats stage, as well as the stupidity of computer controlled players. Play a match against a computer player, and as the match begins, start fighting your opponent on the Pokémon's right arm (his right, but it's actually to the LEFT of your screen. Keep your opponent busy fighting on that arm, and when the next Pokémon floats by overhead, jump up and leave your opponent behind... He'll just stay there, causing his own death.

Trophy Time
A detail from Classic mode, during the "Snag the Trophies" bonus level. If you step right up to the trophy "funnel", you can pause the game and zoom in to just barely see that the bottom of the funnel is the Smash Bros symbol.
Submitted by BlueEyes

Strange Settlement...
There appears to be a tiny village or something here in the Rainbow Cruise stage... Just after the ship falls and you need to start hopping on the platforms, pause the game and zoom in. On a green ledge in the mountain background, it almost looks like a small group of structures. Not sure what this one's supposed to be...

Creatures from Crates:
I've gotten quite a few e-mails, from people asking why Goombas, Topis, ReDead, and Oktoroks sometimes pop out of crates during a battle. As far as I know, it's just something that the game does randomly. These characters don't seem to appear very often. Maybe there is something special you need to do before one of these creatures will make an appearance. But I think it's just random....

Koopa & Purin
Something interesting happens when you change the game's language to Japanese... Bowser will become Koopa, while Jigglypuff will be known as Purin. These are of course the Japanese names that are used for these two characters. It's just neat to hear the crowd chanting "Koo-pa! Koo-pa!". As veterans from the original Super Mario Bros will remember, Mario's nemesis was originally known as Koopa. He returned as Bowser in Super Mario Bros 3, and has gone by that name ever since.

Swinging Sensation
Something that I'm sure many players have noticed, is that each character has their own unique way of using a swinging item. For example, Sheik's smash move with the laser sword involves a double swipe move. Captain Falcon stabs forward when he smashes with a swinging item. As for running attacks with the beam sword, Luigi does a floor dive, while Mewtwo does an impressive twirl move with the sword spinning in midair. Just another one of the many cool details found in this game.

Virtually Unnoticed:
Another small detail happens when you change the game's language from English to Japanese... If you have a look in the trophy room, you'll be able to spot the Virtual Boy. The Virtual Boy didn't catch on in America as well as Nintendo had hoped, so they've left it out of the English version trophy room.

Speeding Sign:
In the Onett arena, everyone hates that damned vehicle that races by and hits you when you're in the middle of a battle... But there's actually a sign warning players of the danger. You can zoom in on your character when you're all the way to the right of the stage. From there, angle the camera to read the 'Onett Message Board'. The sign reads:
CAUTION: A black van driven by this guy has been spotted racing recklessly through town. Be careful.

Submitted by Arvid "Olimar" Keemink