What needs help/added/ or changed IMO:
1. Adventure Mode*
--The story sucked. Expected a lot more from someone who wrote the Kingdom Hearts scenario.
2.Game Mechanics**
--There are some maneuver that can still be implemented to change things up a bit, like:
----Air-Grabbing
----Under stage/ceiling approach (ex: Zero Suit Samus uses Plasma Wire to "vine swing" under stages if she passes the magnetized point at the edge of stages with Plasma Wire. Link would "web-sling" with Claw Shots", and Samus with her Grapple Beam. Sonic would just run up-side down instead of falling)
--Some characters could run on vertical planes on stages like Shadow Moses's watch towers when dashing, like Captain Falcon, Luigi, Mario, Sheik, Sonic, and Zero Suit Samus.
3. Character Properties**
--More uniqueness exclusive to individual characters (Lucario having the Aura-power build-up, Ice Clmbers being a pair, Zelda/Sheik transform, Zero Suit/Samus switch)
----Someone mentioned if Mewtwo were to return, he would have something unique like forcing opponents to have a higher stale move negation rate, which is win by the way.
--Altering characters (Chairzard could use multiple jumps, Olimar could be less dependent on tether recovery and Pikmin, Bowser is able to use a tether recovery-- like a chomp)
--Updating character's move set (ex: Samus can have Ice Missiles from Prime 3: Corruption, Toon Link can have Bombchus, Deku Leaf, Grapple Hook from Wind Waker)
4. Newcomers and Returning*****
--Toon Link (Out): If he doesn't get the boot like he should, making him completely different from Link would be neat. Like I mentioned earlier, he could use a grapple hook, bombchu, and deku leaf while using that as a glide maneuver as he did in Wind Waker.
--Newcomers: Captain Rainbow, Dixie Kong, Issac, King K. Rool, Krystal, Ray MK II.
--Returning: Mewtwo, Roy
--Hopeful: Main Fire Emblem protagonist that doesn't use a sword and have blue hair, while replacing Toon Link with Midna.
--Third Party Guest: Megaman, Yoda (DON'T JUDGE ME!)