The problem is that some characters are probably going to be eaten by the impending drought monster...by that I mean, "hasn't had an appearance in a long time". That will be deadly for some. Krystal comes to mind, especially if she gets retconned from Star Fox. Isaac could get eaten as well.
The problem isn't the amount of characters available as much as it is the quality of characters available.
Some cool ideas for future Smash newcomers include Tom Nook, Isabelle, E.Gadd, Inklings, Wonder Red, Captain Toad...It's when you take every fan rule and apply it that makes things look bleak. If you let your imagination run wild, you'll come up with some cool ideas!
Wonder Red would be an amazing character because of the several abilities in W101, but the fact that nobody believes in him because the game bombed screws him over. Inklings also have a plethora of content for a trap/stage control moveset, and they are much better off as a healthy series.
E.Gadd is an off the wall choice, but using a custom Poltergust with elemental powers, he'd have a unique moveset for sure. Tom Nook has his sacks of bells and furniture...Isabelle...there's got to be something she could do to be different.
Captain Toad could stun players with his searchlight similar to Mewtwo's Disable, could use a minecart similar to Jr.'s side B, and he could use the pickaxe in his moveset somehow as well.
Chibi-Robo is another. With the new abilities he is getting in Zip-Lash, he'd probably have a fun moveset for sure. He'd easily have a tether recovery, could shock people with the plug.
This is just scratching the surface, and each is one that really isn't often talked about aside from Captain Toad and Inklings. That's...5, aside from a new FE character, new Pokemon character, DK characters, or 3rd parties.
YOU THOUGHT I WAS DONE?! Well, I mean, I did too. Until I came up with more ideas.
Bandanna Dee has different abilities with his spear. Recovery could be like a helicopter, lotsa stabbing, etc...
Isaac is Isaac. Psynergy and Djinni. My only fear is that he'll be eaten alive by the drought monster.
Add Snake back for his moveset and notoriety, then you could always add Rayman as another notable 3rd party. Long range physical attacks with his floating body parts. Could be fun. Play Rayman Legends if you need more inspiration.
So now we're at what, 9? Add the usual Pokemon and FE character to get us to 11. Add K.Rool or Dixie if they aren't added yet, maybe Wolf, and you've got 15.
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Interesting topic change here...but let's talk hypothetical. Now, it's been confirmed that current in-game content doesn't change chances for anybody, but...what if it did?
So for example, because of their costumes, K.Rool and Inklings are doneskies. That would eliminate two leaders from the running, likely making our Top 5: Wolf, Bandanna Dee, Isaac, Snake and someone else in the mix. Isaac maybe?
What happens then?