For Wild Mass Guessing concerning specific games in this sub-series, see the below links: Wild Mass Guessing concerning the series as a whole.
Mario and Luigi will eventually team up with Donkey Kong.Bowser and King K. Rool will also join forces to fight the trio.
Starlow is mean to Luigi because she secretly has a crush on him.Starlow finds Luigi's shy, awkward demeanor to be endearing, and treats him like a loser as a form of romantic teasing.
- She says that Luigi has a sweet moustache in Paper Jam as part of her pep talk. She wants to admit more to him but she just can't because they're different species.
The next game will have Peach teamed up with Starlow as a playable character.As a single character, I mean. We know from a few games that Peach has SOME platforming skills, and the last two games reveal that wish power with Starlow is powerful enough to lift an unconscious Bowser and toss him aside, and later stop Bowser from using the Dream Stone and then destroy it! And with Peach being playable in ANOTHER recent game, it's only inevitable. Plus this gives another sort of justification for giant battles: Peach can just wish for a giant robot or for someone to become giant or something!
One of the next games will feature the Massif BrosFawful was super popular and got promoted to Big Bad before being killed off, Popple and Kylie Koopa got brought back because they were popular and the series really likes bringing back Ensemble Darkhorses, so it seems kind of logical that the most popular non villain characters of Dream Team are likely to end up in one or both of the next two games in the franchise. And their jobs as tour guides makes it even easier to explain why the heck they might end up on the other side of the world for no apparent reason.
Bowser suffered brain damage during Superstar SagaEarly in the game, Bowser gets amnesia after being shot out of a cannon, becoming Popple's apprentice "Rookie". He regains his memory in the middle of a fall from a great height, right before he hits the ground and is knocked unconscious. It's highly likely that one or both of these events gave him brain damage, resulting in his less-than-bright behavior during the rest of the series (including his failure to recognize his own past self in Partners in Time). He may be recovering as of Dream Team, going by his increased suaveness and his recollection of Luigi's name at the very end.
Bowser Jr. will never appear in the series.Besides his appearance in Dream Team.
- From the OP, jossed. He returns in Paper Jam.
Fawful and Popple are the same person.Okay, this is a big stretch. Like, Epileptic Trees big. But the only game that Fawful and Popple shared was Superstar Saga, when Fawful was just a lackey, so it would be understandable that he could appear all over the place like Popple does. Popple doesn't appear in the next game, but Fawful does in the Mushroom Kingdom sewers, hiding. Popple might not appear in Partners in Time because Fawful in in the sewers the whole game. Next, in Bowser's Inside Story, Fawful is the main villain. Popple doesn't appear in this game because Fawful was busy trying to take over the world. Finally, in Dream Team, Popple finally reappears, but Fawful is nowhere to be seen. What if the reason Fawful isn't there is because he was laying low after his defeat in BIS and didn't want to be caught, so instead he acted as Popple in Dream Team. Fawful's engrish and Popple's thick accent might both be faked. They're both beanish, and they both like to grin a lot. Of course, you'll have to believe the theory that Fawful survived the events of Bowser's Inside Story, but still...
E. Gadd in these games is Fawful in disguise.In Superstar Saga, Fawful sets up a café because he secretly wants to overthrow Cackletta. He tries to get away before the Bros come, but fails and is defeated. In the next game, the real Elvin Gadd invents a time machine. Fawful then kidnaps Gadd while the bros are stuck in the past. Fawful also runs a badge shop as a side business, genuinely not recognising the baby Bros. he met for himself. He also spies on the brothers with Stuffwell, explaining the E. Gadd time travel memory sequence. In the next game (similarly to the above WMG) Fawful is too busy to pose as E. Gadd, and the real E. Gadd moves back to Boo Woods in time for the events of Luigi's Mansion 2. For all subsequent games, Fawful is dead and E. Gadd is away. If E. Gadd comes back, he moved back, and if Fawful comes back, he wasn't dead.
M&L 6 will feature a pair of characters controlled separately from the Mario Bros.Superstar Saga had just Mario & Luigi, Partners in Time had Mario & Luigi accompanied by their baby selves, Bowser's Inside Story had Bowser, Dream Team went back to having just Mario & Luigi and Paper Jam had the Bros. joined by Paper Mario. So following this pattern, the next game will have a playable character/playable characters that don't fight alongside Mario & Luigi. And since two games featured two characters, two games featured three characters and only one featured four characters, I predict that we'll get a pair of characters. My best guess would be the Wario Bros.