-Midna: Zelda needs more characters, no way around it. Midna herself is a one-off character, but she's arguably the only one of Link's companions that's more important to the story of her own game than Link himself, and she doesn't suffer the same problem as other characters like the champions from BotW, or the OoT sages in that she really doesn't compete against characters from her own game. I can definitely see her be somewhat of a Glass Canon, very much a lightweight, but with ridiculously powerful abilities and hard to approach. It also helps that she's one of my favorite Zelda characters, so yay, haha.
-Waluigi: Honestly? I think he's overrated as ****, but considering the Mario characters already in the game, he makes sense. He's pretty much the only non-generic, heavily recurring Mario character left to be playable in Smash, so his inclusion would simply feel right. His only barrier is moveset potential to be honest, as they'd pretty much have to make **** up from the start, and he doesn't really have the right "build" to take moves from any other character. But it's definitely doable, and they could give him moves that represent his personality more so than his physical abilities, like they eventually did with Luigi.
-Krystal: Star Fox could use another character. I don't think it needs one per-se, but considering Krystal is an option, it honestly feels kind of like a no-brainer. She'd play absolutely nothing like the space furries already in the game, so it would be a great way to expand Star Fox representation. She wasn't playable for long in Adventures, but they can extend her moveset to cover everything Fox did in that game to create a pretty unique fighter.
-Zero: Probably the most famous Mega Man character apart from Mega Man himself. He not only has a wide variety of moves to take from, but he's even appeared in other fighting games, which would make his inclusion perfectly natural. There's already characters that fit what I imagine would be his gameplay archetype, and he doesn't have any interesting "gimmicks" to offer, but nonetheless, I think he could be a ton of fun to play as a fast-paced swordfighter with a ton of mobility and a few ranged special moves.
-Isaac: I've been a huge supporter of Isaac since Brawl was announced. Golden Sun is basically the game that introduced me to JRPGs, and I absolutely freaking loved it. I can't really say anymore that it's my favorite RPG of all time, but it still holds a super special place in my heart. Additionally, there's a lot of things you could do with his moveset. He could be unique in that he's a swordsman that has his sword as little more than an accessory. He could have a wide variety of ranged elemental psinergy attacks (or just stick to Earth-based abilities, either would make sense), moves involving the characteristic floating psinergy hand, and of course, a unique mechanic involving Djinni and summons. There's a lot of options when creating a moveset for Isaac, and there's several ways to do it right. He doesn't just have moveset potential. The potential is ****ing endless.
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