Alright, so, on today's episode of Overthinking Everything, I'm going to fenagle a new theory for everyone's amusement that I will call "Continuation" theory to possibly predict the last two newcomers.
In Smash Ultimate, the trailers have been very heavily thematic in comparison to Smash 4. The Banjo trailer that we got recently is a prime example. DK, Diddy, and K. Rool were all previous RARE characters and, of course, so was Banjo. Duck Hunt was there because of the very obvious animal duo pairing. When it comes to the character choices in the trailers, it seems to be very deliberate and with purpose. Simon/Richter's had Luigi as Nintendo's go-to character with spooky games. K. Rool obviously had DK and Diddy but King Dedede, the only other major Nintendo character with King inherently in his name, was there too. Ken/Inceniroar's was "fighting" characters with Little Mac from the get-go and then all the characters in the game with boxing gloves (Villager, K. Rool, and Bowser Jr.) as comic relief. Hero had Link, Metaknight, and Marth in prominent roles because, well, swords while Isabelle and Joker's trailers basically focused on the individual characters themselves. This then leads to an interesting observation about the first full character trailer we got, Ridley's...
The main characters in Ridley's trailers are Mario, Megaman, and Samus. The connection between Samus and Ridley is obvious but what about Megaman and Mario? It doesn't help that Mario and Megaman are "killed off" very early in the trailer and the connection between Samus and Ridley is extremely highlighted. This is where the Continuation Theory comes in. We don't exactly know what happens to either of them. Megaman makes the classic death noise but he doesn't explode so he's probably seriously hurt but not necessarily dead. Same could easily be said about Mario. Chances are, they're simply somewhere else in the environment. Why is this significant? It's because we never really get a proper conclusion to Samus and Ridley's fight. Samus is about to dive kick Ridley in the face and then it just sort of fades out. This makes me believe that this story will continue but why? Because it's already happened once before.
The ending to K. Rool's trailer is very vague as well. A big clash of fists, a shock wave, and then we don't really see what happens after that aside from a goofy little skit at the end. At the start of Banjo's trailer, their story continues. I noticed that the endings of Simon/Richter's trailer and Ken/Inceniroar's trailer are kind of vague too. Luigi is about to go into his body when Carmilla appears and we don't see what happens next. Inceniroar gets a line of challengers, utters a sigh of annoyance, but we don't see the end result. There's a decent chance that the story of at least one of these trailers will continue, with my money being on the Ridley trailer being the most likely. Before I go into that, let's imagine the other two.
With Inceniroar's, the end result is that he probably effortlessly beat his three challengers and is looking for someone to give him a real challenge. Who could do this? Keeping with the theme, it would probably be a character from a fighting game. For example, thematically speaking, someone like Heihachi from Tekken would work really well here although that is just one possibility.
With Simon/Richter's, we have Luigi as a ghost/spirit and we're still in the spooky locale of Dracula's castle. This makes me believe that, if this story continues, they would try to have a character that fits this theme. Off the top of my head, two characters fit this theme pretty well: someone from Resident Evil (probably Leon or Jill) or someone from Yokai Watch like "Nate" with Yokai like Pokemon Trailer or someone stand alone like Jibanyan coming to save Luigi.
Now let's go back to Ridley. Like I asked earlier, what's the connection between Mario, Megaman, and Samus? I looked into Smash's past and looked at past presentations:
Bowser Jr's trailer is the only character trailer in Smash 4 where all three characters were together in the cinematic. It's kind of the same premise too, they're fighting a villain but this time they're fighting a Mario villain. Coincidentally, Mario and Megaman get hurt in this trailer too. Beyond that, there's one other time: the Final Smash 4 presentation.
At 15:37, you see "Geno" fighting Zero Suit Samus. At 15:40, you see Samus, "Geno" and Megaman together. At 17:00, you see "Geno" fighting on Ridley's stage, the location that most people agree is most similar to the one in Ridley's trailer. Tin foil hatty but there's a proven historical connection between these characters under this train of thought. Again, the characters for trailers seem to be very deliberate if the characters are given significant screen time. Based on this, these characters were probably put together for a reason but the full reason may not be obvious because we don't have the full story yet. Following this theory, the connection between the characters will be better established when the story continues and a lynch pin that connects these three characters is Geno. Still, this is kind of out there but I wanted to see what people thought of it.
Oh boy, that Nintendo Direct CAN'T.COME.SOONER. 
