Newcomers: Captain Toad, Dixie Kong, Funky Kong (clone), Daitoryo, Takamaru, Sylux, Bandana Dee, Decidueye, Alph (clone), Elma, Rex, Inkling, Bomberman, Rayman, Steve (13 plus 2 clones)
Returning: Ice Climbers, Wolf (2)
Captain Toad: A fairly popular and extremely recognizable character who has appeared in all of the last three mainline Mario games. Not only that, he's the star of his own game now, which is set to appear on not one, but three Nintendo consoles. He is the newcomer I'm most confident in predicting. (Certainty High)
Dixie Kong: A popular character from a popular franchise that everyone seems to want a newcomer for. Given Tropical Freeze's re-release on the Switch, I think it's fair to say that I expect her. (Certainty High)
Funky Kong: Hear me out. Every game has had clones, and I don't expect that to change with Smash Switch. Given Funky Kong's newest appearance as one of Tropical Freeze's five playable characters, he might just be in the perfect scenario to be considered for the last-minute clone treatment. I could see him being a less grab-oriented DK with better aerial movement and juggling. (Certainty Low)
Daitoryo: I do not believe that I'm crazy in seeing a pattern of retro and historical characters. Each game since Melee has included one throwback "retro" character (Ice Climbers, Pit, Little Mac) and one character that highlights something about Nintendo's history (Mr. Game and Watch, R.O.B., Duck Hunt). If this pattern continues, I believe that the stylized depiction of Napoleon from Nintendo's "President" style Hanafuda cards is a great choice. That said, I did not see Duck Hunt as a potential historical character at first despite the game's origins as an early arcade game and its significance to the NES's success, so I fully admit that I could be wrong. Consider him something of a placeholder for the history character. (Certainty Low)
Takamaru: Ever since his appearance as an assist trophy, we've been keeping an eye on Takamaru for this next game. Given that his game was released overseas (finally), and given that Hideki Kamiya has acknowledged that he would be interested in working with the Murasame Castle franchise, I could see Sakurai picking him. That said, he's not the only contender for a retro spot, and we're not guaranteed a retro in the first place. (Certainty Moderate)
Sylux: The Metroid series is seeing a significant amount of attention, and Sylux is the villain candidate who seems most probable given Sakurai's stance on Ridley. I fully expect Sylux to play a significant role in Metroid Prime 4, and it seems to be the perfect chance for the character. That said, he hasn't had a huge role yet, and it could be a bit too early for him. Further, a Metroid character, while a popular choice, is not a guarantee, and there's always the possibility of Sakurai coming back to Ridley again. (Certainty Moderate)
Bandana Dee: The Kirby series has done very well recently, and Bandana Dee has been very consistently appeared as the fourth playable character or in support roles. And remember, the Kirby series has had a main series release every year since 2014. He has very little going against him. If he's not in, it's because the Kirby series isn't getting a newcomer for some reason. (Certainty High)
Decidueye: Admittedly something of a placeholder, I wouldn't be surprised at all to see this very popular starter in the next Smash. A flying grass-type archer, it has plenty of moveset potential, and it's been the poster boy of this gen. That said, it has a lot of competition from within its own series, and it could be passed over in favor of a newer Pokemon. (Certainty Moderate)
Alph: An off-the-wall pick from me, but I could very easily see Sakurai revisiting the idea of making Alph a clone who uses shield-breaking Rock Pikmin. And, again, clones don't take much development time, and I expect us to have a couple. (Certainty Low)
Elma: A unique, popular character from one of Nintendo's newest series, I could definitely see Elma making it into the next Smash Bros. Her game is likely to receive both a sequel and a port in due time (XCX ended on a cliffhanger), and her game was one of the best received on the Wii U. That said, she faces the distinct possibility of being shafted in favor of Rex instead of being added alongside him. However, I'm leaning towards both of them being included, especially since Elma arguably represents an entirely different series from Shulk and Rex. (Certainty Moderate)
Rex: While I'm unsure whether Rex will fight alongside Pyra or with Pyra in the background, I'm pretty sure he's on Smash's radar. That said, he does share many traits with Shulk, namely in his swordfighting style, and he faces very real competition from Elma, who could potentially be added before him. If he is passed over in favor of Elma, I expect him as DLC. (Certainty Moderate)
Inkling: Duh.
*Bomberman: Definitely the third party I'm least certain of on my prediction roster, but he's still undeniably iconic, popular, and requested. Given that he had a launch title on the Switch, I can see him happening. (Certainty Low)
*Rayman: While I'm not certain on him by any means, I think it goes without saying that Ubisoft has been very close to Nintendo. He's probably the most likely new third party, if you ask me. (Certainty Moderately Low)
*Steve: I've stated my case for him before; he's iconic, his game is the second best selling of all time, he's had a release on the past three Nintendo consoles, and Nintendo is willing enough to talk with Microsoft historically to let the Super Mario Mash-Up Pack happen. I think he's a slept on third-party, and I don't think I'm crazy to predict him. That being said, the character has a notable hate-base, and Minecraft isn't quite the titan it used to be. (Certainty Moderately Low)
*I'm hesitant to say who the next third party characters will be, and I expect to be wrong. My guess on how many we'll see is three, but I could be wrong on that as well.
Ice Climbers: I mean, the only reason they weren't in Sm4sh to begin with was the 3DS. (Certainty: Highest)
Wolf: Very popular, a veteran, and easy to bring back. (Certainty: High)
Spring Man: I know, I know, let me explain why I have him as DLC. While Rex is also extremely new, he has the benefit of coming from a series that was well-established and close to Sakurai's heart. ARMS does not have that, and there was no way for Sakurai to know ahead of time that ARMS, or even the Switch for that matter, would be such a success. I think he has seen the demand for an ARMS character, and I think it will happen in time, but I'm leaning towards seeing him as the Mewtwo of this Smash, the first DLC character released. That said, I could be wrong, and I could see him making the base roster as well.