Something that always bugs me about Special Mode, is that in a giant battle EVERYONE beccomes gigantic.
Which is okay, but honestly, I'd prefer to be able to choose which character can become gigantic and which won't.
For example:
P1: Normal Size
P2: Big Size
P3: Small Size
In my opinion, this would work better when doing challenges, because you can make the opponent has the advantage or the disadvantage.

Just an Idea that popped out of nowhere:
Remember the Classic Mode in Melee? Remember those 2vs2 fights against you (and an ally) against an enemy team?
Well, considering that Melee selected a random team among a list of teams, I think we can do the same in the game's Classic Mode.
Ex:
-Your character and Random Ally vs. Team Mario and Peach.
A list of teams and combinations I tought of:
-Wario & Bomberman (Both starred in a crossover game called Wario Blast)
Stage: Bomb Factory
-Meta Knight & Black Mage (both have similar designs, and both appear in the "Nightmare in Dream Land" event as foes)
Stage: Lunar Core
-Donkey Kong & Wario (Both debuted as Mario's enemies)
Stage: Gangplank Galleon
-Chibi Robo & Bomberman (Both being robots)
Stage: Nintendo 3DS
-Goku & Naruto (Both are Shonen Anime Protagonists and wear orange, not to mention that both use energy based attacks)
Stage: Hidden Leaf Village
-Megaman & Sonic (The Blue Bomber and The Blue Blur)
Stage: Central Highway
-Tails & Fox (Both are Foxes duh)
Stage: Casino Night Zone
-Marth and Lloyd (Swordsmen)
Stage: Castle Siege
-Kirby and Jigglypuff (Pink Puffball and the Balloon Pokemon)
Stage: Dream Land
-Princess Zelda and Black Mage (Both are magicians)
Stage: Hyrule Temple

After analyzing the Classic Mode, I tought of something:
-The fact that you can see all the enemies you will encounter right at the beginning kind of kills the surprise of waiting for an opponent.
-It seems that there are no enemy teams available in this mode, and that's something that every single Smash Bros game has had.
I'll just quote myself from the General Speculation:

-One last thing, it would be kind of interesting that one culd win trophies or other collectables (if there are any) by beating Classic Mode Stages. Mostly because it works as an encouragement to not lose your battle or you will lose some of them.
Just some ideas I wanted to drop by, I'm not saying they should be in, but I'd love to see them.