My change would be... Inkling as Smash 4 DLC instead of Corrin. They would have been way better received, and freed up a slot for Dixie in Ultimate
Not really. Dixie not getting in isn't because of another character suddenly gone. We don't know why she has yet to be in, as a semi-clone, Echo, or something else.
Inkling also would've never worked on the 3DS. S/he's too mechanically intensive. It would've been a much more shallow moveset compared to what we got. Not that they'd be a bad choice or anything like that at the time. Just not feasible. This is probably why, despite being an easy choice, was only a Costume to begin with. Someone like K. Rool could've been way more feasible in comparison. Or even Isabelle as a semi-clone of Villager(albeit, a newcomer not being reasonably unique probably wouldn't have been the best way to go about DLC, hence choosing all the newcomers who aren't some kind of clone. Sure, they may have used a base, but they're about as clone-y as Ness is to Mario. That is, not at all).
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As for my change? Honestly, this is difficult. I really like all the characters overall.
That said, I do agree with Peach not using Toad, but otherwise, uh... I guess I can't really think of any I want to change otherwise. I'm quite happy with Hero(despite wanting Slime more), and even another character I wasn't interested in instantly meshed with me(Palutena). Like, the only one I raised an eyebrow on originally was Wii Fit Trainer, but I definitely wouldn't replace them either. Closest I guess is I'd love Shy Guy to be in instead of PP, if only for another Yoshi rep too, but regardless of the Universe, I love the little guy. Still, I love PP too, so I'd rather a newcomer.
I admit I would like to see Young Link reference MM more, but not to the degree of completely changing how he works. That would ruin his playstyle, and I don't want that. I do wonder, related, how Peach could be fixed up enough to remove Toad but not change that much. Just use Toadsworth now, I guess? That doesn't work during Melee, though. Then again, it's unclear if it's a generic Toad or the main Toad. So that doesn't help much. XD