What do you think Luigi's friendships with DK, Toad, and Peach will be like in the sequel (and maybe Yoshi, if he's introduced)? We saw very little of their interactions in the movie so there are lots of possibilities.
No kidding. One of the things I'm most looking forward to in the sequel is Luigi properly interacting with the rest of the cast. Poor guy was in a cage for so much of the movie that he barely got a word in with anyone besides Mario.
Donkey Kong seemed to like Luigi from the get-go, but if DK and Mario continue to have tension between them despite how many times they've saved each other's life, Luigi's going to get roped into that tension, even if he just ends up as a guy on the sidelines begging the two of them to chill. I see a relationship between Luigi and DK as friendly but strained, with Luigi siding with his bro while understanding the gorilla is a good guy at his core, and DK not taking Luigi even remotely seriously in a "condescending big brother" sort of way.
I'm pretty certain Luigi and Toad would get along great. Movie Toad is just pure friendliness, easily enamored and endlessly excited. He and Luigi also fill the same sort of role: not much of a fighter, but happy to help out in every little way they can, with the big difference being Toad craves excitement while Luigi wants to avoid it. I can envision them forming a bond of mutual admiration, with Luigi envying Toad's confidence while Toad admires Luigi's physical abilities which... whether he recognizes it or not... aren't too different from that of his brother.
Princess Peach and Luigi have great friendship potential, but I can easily see Movie Peach accidentally getting overprotective of Luigi. She was already pretty protective when it came to Mario, even as he proved his strength and competence over the course of the film. This was for good reason of course, but it's clear Princess Peach is dedicated fully to two things: helping those who won't back down, and guarding those who don't want any part of the fight. Heck, her royal duties revolve around ensuring a civilization that can't hold up in the face of conflict is able live out a life of peace and contentment, so it'll probably be new territory for her working with Luigi; utterly terrified, yet willing to put himself in harm's way for those he loves. I'd really like to see that.

















