Mario and Luigi's brotherly bond, full-stop. While their sizable age gap makes their dynamic seem more like father and son at times, they’re clearly the best of pals and care a great deal about each other. They even have a special handshake that they do several times throughout the film.
Mario Bros.: (when doing the handshake) Heyyy, glug-glug-glug-glug-glug!!
Luigi's obvious crush on Daisy makes his interactions with her adorably sweet, especially when he can't figure out what to say. Mario then helps out by telling her directly and offering her a ride, then good-naturedly teases Luigi about almost letting her go.
When Luigi is about to leap into the unknown to go after Daisy across a chasm that would kill him otherwise, he gives Mario a kiss before taking the leap.
Everything about Daisy and Yoshi’s interactions. Daisy is the only person to treat him with kindness, therefore he gets attached to her rather quickly. This culminates in Yoshi saving her life when Lena tries to kill her, by using his famous tongue yank.
After helping save the Mario Brothers from Lena and the Goombas, Big Bertha kisses Mario, who sincerely thanks her for the help.
Random as it is, Iggy & Spike do genuinely switch sides and become Daisy's loyal supporters, helping reintroduce her to her father.
When Daisy is reunited with Daniella in the Mushroom Kingdom. Ever since her abduction, she'd be scared and alone in a very creepy world. Daniella, who only met her once before, hugs her and introduces her to the other kidnapped women, who clearly had gotten to know one another and banded together during their imprisonment.
The scene where Luigi and Daisy say goodbye.
Mario: (to Luigi) She's tryin' to tell ya she can't leave until she knows where she belongs. And if you loved her, you'd understand that.
Mario and Daniella's relationship is very sweet and sincere, especially in the escape scene and ending where they're living together.
