While I love a lot of the Final Smashes, I can't help but feel disappointed by others. Here are some that I feel need to change, and some ideas on how to change them.
Copied Final Smashes
Falco: "Personally, I prefer the air" says Falco, getting into a Landmaster. Why he couldn't call an aerial strike is beyond me.
Toon Link: Triforce Slash is already an uninspired, boring Final Smash. Giving it to Toon Link along with Link is just too much. Toon Link should've used the Ballad of Gales, where he plays the song and proceeds to fly up into the air in the King of Red Lions before crashing back down.
Dark Pit: The Dark Pit Staff was never some kind of superweapon in Uprising, so why is it in Smash? Really, they should've incorporated the Lightning Chariot, which Dark Pit used on a few occasions.
Lucina: Honestly, even a visual difference would've been enough to excuse the same Final Smash as Marth. All we needed was some kind of cut-in where she shouts something like she did in Awakening.
Sheik: Using the Light Arrow was fine when she was still part of Zelda, but now that she's apart, she could at least do something different. Maybe use the harp, or something generic based on ninjas.
Original Final Smashes
Rosalina & Luma: "The Final Smash of Minor Annoyance" - maybe they could incorporate the Comet Observatory, or the Galaxy end-game black hole?
Mario: "Let's take the most iconic character in the history of gaming, and just give him some kind of big fireball attack because he uses fire" - they seriously couldn't think of anything from the dozens and dozens of games he's been in?
Link: Once again, Triforce Slash is pretty dull.
Peach: It just seems so boring. Her name is Peach, so she drops peaches. Why not use her... wild emotional changes... from Super Princess Peach.
Mega Man: Kidding, of course. His is perfection.