I think that would go into this forum.
Suggestions

How about a slots mode like in Mortal Kombat 9. Where there's this slot thing that pops up before you start the match that gives random buffs/debuffs/status to the characters, on top of stage modifications like raining fireballs and such.

Good for s*** and giggles I'd say.

Stamina Mode

Mirror Mode
Stage: Final Destination
Character: Any
You're only allowed to pick the character you play as in this mode. After that you're taken to FD and on the other side of the stage a whited out version of the character you picked will be there. They mirror any inputs you press.

Rpg mode: Your character has a level/stat system. The rest is up to the devs where it's used.

I think Final Form Mode could be balance by this:

Character Specific Special Versus: Can apply Special Versus modifiers for each character. Include a option for Final Form mode(Does nothing if the character you pick doesn't have a Final Form). You could have Giant Turbo Vampire Egg Marth vs Vengeance Bankai Ichigo.



Boss Rush Mode: Fight all the Adventure mode bosses, plus all of the Final Forms. For the Final Form battles, you get a level 9 CPU ally. You could also get a CPU ally if any of the Adventure mode bosses are over-the-top hard.

Special Classic/Special Boss Rush Mode.
Special Classic: Some of the levels will have other special modifiers besides obvious ones like Giant, Metal, etc. Turbo enemies or Dramatic. On Intense, Final Forms could have a small chance of being a stage enemy or maybe the boss stage before Master Hand.

In either case you'd probably get an ally or 2.
It'd be like these:
1p Mario and L9 CPU Link vs L9 CPU Turbo Marth.
1p Mario and L9 CPU Freeze Link vs L9 CPU Mega Turbo Marth and L9 CPU Mini Dramatic Vengeance Captain Falcon
1P Mario, CPU Link and CPU Kirby vs Level 9 CPU Super Saiyan Goku.

Special Boss Rush: A ridiculous version of Boss Rush that unlocks after clearing Boss Rush on Intense. Special Versus modifiers will randomly be selected for each boss. If they're given a large number of these then some will be negative modifiers. If it ends up being too hard then the player gets random CPU allies. No Turbo bosses besides the Final Forms though probably ( unless there's regular character style bosses like Metal Mario in 64).


Smash Flash Run: I think the devs would make Smash Run turn out awesome in SSF2.

Maybe there could me some sort of minigame or something where the players must keep a number of balls floating in there. Whoever attacks one has the ball changed to the player's color, and as long as the ball is in the air, the player who "owns" the ball will gain points.

Over time, the number of balls in the air shall steadily increase, and in addition the stage will move. You must keep on your toes if you want to have the most points.

Cool little concept, huh?

Kirby, MK, Jigglypuff OP.

For Smash 64 mode, additionally all techs are disabled and you can Z-cancel every aerial.

Capture the flag.

big a** stage, 4 player team match, flag item, what could possibly go wrong?

This might sound a little odd but I imagined like a Stage Builder style Classic, where you organize and create a personal classic mode. (In the instance you wanted to show it and goof around with your friends), you know just organize what matches are where, or have it randomize between a few select characters, put what level AI are in what matches, heck there could even be the possibility of making all metal matches where all your opponents are metal. Of course unless it was a prerequisite to unlock something it would just be for fun. I could imagine having the ability to export them and share online.

Another concept is like a mini-game concept hot potato style, and see how long you can juggle a ball while surrounded by bouncy walls, and as the ball gains percent it becomes faster and harder to juggle, possibly if you somehow get it to 999% it adds another ball, and so on, and perhaps the option to automatically start with more balls like a difficulty select? This would go in Stadium and the score would be the time.
Edit: I read a bit above me and noticed this concept is similar to the basketball concept, while they're not exactly the same, and I'm not removing it, I felt like I should point out I did not take it from anyone, it just happens to be similar.

In a similar style as All-Star mode where you select a character from a series, you have to fight and beat characters from other series, as you progress some matches could possibly contain allies from your series, if you have no one else from your game/Anime/Show in the game, then it will select a previous character you beat as an ally. Kind of like a faction battle.
To make it more interesting, the mode could be two player competitive, and if you game over, you lose the chance to beat the AI you were fighting, but still continue until the end., and whoever conquers the most series by the end is the winner, the series you beat wont be randomized, you could possibly choose individually, or go down a preset path maybe? And ones with a lot of characters such as Mario may be worth more. I'd assume a certain number of matches would be allowed. if the score is even the players fight to decide who wins, Also possibly the ending to this mode could be series based, like if there's any character animation it may show you on your stage with whoever may be from your game/series.
In a one player scenario you may have to face AI opponents who make decisions to conquer others as well? Or it could just be a non competitive All-Star style run, but series based, or you would have to score enough points.
There could be difficulties set with this, and maybe even an end boss (If in a two player game, the winner proceeds to fight the boss)

Anyway, I started this post because I thought I may as well share my silly idea, and then figured I could add a bit more in the realm of ideas, and so I just kinda gave out what I thought may be unique or interesting, I put the most time into the last one, as I knew the concept, but putting it into words was a bit more complicated, when I think it needs to be explained to others.

Feel free to ask about how a mode would work in a certain way, point out a flaw, say if I missed something, or tell me when you're confused about something. And I guess just give your opinion on my ideas, saying they're bad wont hurt too much, I just felt like sharing.

Double mode:
You pick 2 character one you play and one who follow you and copy your moves just like Ice Cimbers.

Tag - Hit an opponent and run away until time runs out. Will need a bigger stage for something like that though.

Smash run,All-Star Mode,campaign mode,adventure mode,6 player smash,multi man smash and endless smash.

Flood mode.
There is a custom stage that is narrow and high in vertical length. You have to make it out before the lava/water/oil engulfs you to death. The stage will have a lot of platforms for the characters to remain idle.

Umm this thread is for original mode ideas that aren't in any Smash games not for requesting modes to be put in SSF2.