I'd love a new Final Smash for Mario. The Mario Finale looked cool and would be easy to buff, but it's so NOT Mario. And while I don't care for Mario a whole lot in his own games most of the time (since he's not really a character, he just has an endearing, jolly voice, and if there are multiple character options available, he usually has the most basic attributes), I'd like something that draws from his games a bit more. And I think I finally thought of the perfect one:
The Lucky 7.
Mario's games are all about using power-ups, including the Mario Kart games. It's what Mario is known for. Without power-ups, Mario wouldn't be interesting to use in his own games. Power-ups are also a huge part of Mario Kart, which is arguably more popular than Smash. So why not make power-ups the focus of Mario's Final Smash?
Although I say to use the Lucky 7, which is from Mario Kart, I don't mean incorporate an actual kart into it, but merely that Mario breaks open an Item Box from Mario Kart, and gets the Lucky 7 (this could be a flashy cutscene similar to Captain Falcon's Final Smash in Brawl). The items involved in the Lucky 7 are a Super Mushroom, Green Shell, Red Shell, Banana, Bob-Omb, Blooper, and an Invincibility Star. Of these 7 Mario Kart items, we know 5 are returning for Smash Bros. Blooper and Red Shell are the only ones missing right now. However, Red Shells were an item in Smash 64 and in Melee. They were absent from normal VS Play in Brawl, but were present in the Subspace Emissary. And since the Spiny Shell is in Smash 4, I think it's fitting that the Red Shell should return. As for Blooper, maybe it will be an item yet, but it wouldn't be a stretch to make it exclusive to Mario's Final Smash.
The Lucky 7 would work much like it did in Mario Kart 7. The items would spin around Mario while not in use, meaning he can keep them there forever, potentially, but if Mario gets hit, he'll drop the item. And the player simply has to press the A button to activate/throw the items.
I just think it's the most thematically appropriate Final Smash for Mario, and it would be more effective than the Mario Finale was in Brawl. If they wanted to, they could even change things up. They could add the other Mario items that are in Smash into it, and rename it (similar to how the Lucky 7 has become the Crazy 8 in MK8). Or they could simply make the 7 items he gets completely random, and they could encompass the entire item list (except for crates and what not).
I don't know, it just seems like it would be really cool.