All the Polygons, Metal Mario, and Giant DK playable. Master Hand is too, but solely on Final Destination. All of them work with the natural control system too. Of course, making the Character Select Screen look good is another story. But that's not impossible. You could also having other ways to access the characters by pressing L or R anyway. the issue with the CSS is that it's an uneven number of characters, but they could just position the last 3(Metal Mario, Giant DK, and Master Hand) so they aren't 100% even, I guess? Or give them larger icons so they take up half the space. I dunno. I only see them plausible as playable. MH wouldn't work outside of 1 on 1 fights.
More stage selections too. The other unused stages are available, and grant the ability to use Race To The Finish, but it has its own rules; no time limit, and stocks. If someone wins, the other players just lose their stocks that weren't KO'd in the stage as is. They can be if they hit 300% and are Smash attacked hard enough.
I'd say 1 extra music per stage isn't a bad idea, save the extra stages. So nothing for Meta Crystal, Polygon Cave, and End Stage(to note, I'm trying to stick to their more official terms. The last two I forget the exact name of, but they weren't Battlefield or Final Destination just yet). Also, hazard toggle. Every stage that has a hazard of sorts can easily be removed. Though it varies, of course;
- Princess Peach's Castle removes the Bumper(or it has no knockback and phantom damage?) and the floors don't move. They also could could be equal distance on both sides.
- Hyrule Castle loses the Tornado. That's kind of it.
- Congo Jungle keeps the Barrel, but it doesn't rotate. That or it loses the barrel. Both work. Also, the platforms never move.
- Sector Z loses the ships. That's pretty much it.
- Planet Zebes has the acid never rise. It however still exists, but does no damage in return. It's treated like you're hit with it while at 0%. This actually would make battles easier to survive.
- Dreamland 64 loses the blowing wind.
- Yoshi's Story's clouds don't disappear.
- Mushroom Kingdom removes the Piranha Plants, and you cannot go to the middle pipe. You can however pop back up in the same pipe in return to keep it interesting. The moving platforms are stationary and cannot break.
- Assuming the usage of Race To The Finish, all the hazards are hard disabled. No damage/knockback, etc.
For items, Green and Red Shell are separately toggable, and you can separately select what Pokemon to come out. In addition, all Gen 1 Pokemon from later games are added here(like Eevee). Nothing beyond Gen 1 though, due to the timing of this game.
My only thought on Polygons is they could have a unique option to have any Special Move. Not completely unlike Mii Fighters. However, everybody else stays the same. Maybe you could get currency to buy coins, as well as profiles. So beating the game doesn't entirely unlikely a profile instead. They could add plushes as "trophy" variations, including every tiny thing in the game too. Items, and more. This would make playing through everything way more worth it.
Bonus-wise, might not be worth giving Target Test and Board The Platforms to all 12 Polygons, Metal Mario, and Giant DK. It's a lot of work, and their unique properties require differences too. However, the Polygons could have the same exact specials during these modes, and reuse the same bonuses. This would not count as beating the original character's bonus either. And this means only 4 new bonuses to make. It would also give more to do.
