Biggest one, surprise, is Adventure mode. A lot of people have said something similar, but I'd love it if we had a short, but highly replayable game with plenty of side-scrolling levels and bosses taken from all franchises featured in the game. Add in branching-paths and secret unlockables and the thing could be huge, my ideal would basically be a Star Fox-style structure. Ultimately I couldn't care less about cutscenes, I'd rather just pick a character and go through the whole thing (or perhaps a team of characters?).
Break the Targets. I always felt it was a big Smash staple, it felt extremely weird to see it gone. Even character-specific levels shouldn't be too much effort if they all use generic assets as opposed to Melee/64 when half the roster had levels using unique elements. Custom Break the Targets levels would definitely be the idea.
With Adventure mode being a crazier, experimental single player mode with new features, I'd like Classic Mode to go back to a more basic form. Adding all those crazy features make the "Classic" part of the title kind of pointless. Just make me go through a few fights separated by minigames, add a couple of fun, pre-defined modifiers (such as making X-fight always be team-based and Y-fight always be a 1-1 against a metal character), Master Hand at the end, and we're good.
And talking about Classic mode, I want the return of Race to the Finish! I'd rather see this over something like Board the Platforms to be honest, since it's essentially identical to break the targets except you replace attacking with landing. I think Race to the Finish has a ton of potential though, especially with how Melee introduced several exits to better accomodate the different movement speeds of each character, and a fun risk vs reward element. There's a lot that can be done with this mode, so I was a bit sad to see it was removed entirely from Brawl onwards.
I want new clones to actually be different in playstyle from their cloned character as opposed to having one or two differences. The clone standards got better and better in each game until Brawl, which arguably didn't even have any true clones whatsoever. So I was super dissapointed to see the bar go down with Dark Pit and Lucina, who play identically from Pit and Marth save for a couple of minor differences. I understand that clones only exist because there's almost no work involved in creating them, but you can't deny that there's a difference between Lucina/Dark Pit and the way even Melee handled most of its clones, who despite sharing animations and mechanics, had completely unique stats and properties, leading to characters who felt fundamentally different despite objectively sharing the same moves.
This is not something too specific, but I want Sma5h to introduce a new basic mechanic to the game. Sm4sh changed a few rules, like ledge-trumping, but it didn't really introduce something new that affected the mechanics of the whole cast. Melee added a ton of extra moves, like air-dodges, pummeling, directional throws, side-specials. Brawl added Final Smashes and smaller **** like footstools. Sma5sh didn't really add a whole lot other than changing already-existing rules.
As for smaller stuff.
I want a Mario stage with functioning Warp Pipes.
I want Saffron City, with the random Pokémon door.
I want Sector Z, still by far my favorite Great Fox level (#****Corneria).
I want more, Smash-original stages to be used both as single-player content and as unlockables, such as the Metal Mario stage in 64.
I want Brinstar Depths. Loved the idea of a large, rotating stage. Not only did it not come back, but we never even got an equivalent.
I honestly want Stage Builder to go back to being blocks on a grid. It can definitely be improved, but ultimately it led to better, more consistent results than the touchscreen-based builder in Sm4sh.
I want offline Tourneys.
I want Ice Climbers.
I want Wolf.
I want Snake.
I even want Pichu.
Hell, I want ****ing Pokémon Trainer.
I want all characters in Smash history in one game. I know it's too much to ask for and it's completely unrealistic, but **** it, I want them all.
All these things are ultimately inconsequential though. There's one thing that didn't make it to Sm4ash that was borderline insulting. It absolutely needs to make a comeback. It made the game, and Sm4sh just didn't feel the same without it, making the whole experience objectively worse.
I ****ing need to move the camera in the menus with the right stick.
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