Your headcanons

dude's stuck with junior, he better have a soft spot for kids or his sanity won't endure
 
kamek has a weak spot for kids and nobody can convince me otherwise
He's like the primary kidnapper of kids all throughout Mushroom Kingdom, and he's often stopped by this high-pitched baby-sounding reptile thing (and got beaten up by children) and has to endure that reptile's lullaby soundtracks that everyone sane hates.

I'm convinced he hates kids.

694px-Kamek_and_Baby_Bowser_Artwork_-_Yoshi%27s_New_Island.png


Or maybe just human and Yoshi ones.
 
A long standing headcanon I have is that Bowser invades the Mushroom Kingdom because his own land is desolate, a combination of poor immediate resources (ever see farmland? It's just wasteland), lack of technology to acquire more valuable resources (his kingdom is a rich source of volcanic minerals and such but he doesn't have extraction and stuff; ever see those in World 8?)), poor resource management (anything extravagant is from stolen or plundered things and Bowser is clearly a dictator who rather hoards what he gets), and poor negotiations (Bowser would rather invade than negotiate trade; Mushroom Kingdom often wants to trade and provide disaster aid and such but Bowser almost always rejects it because he's too proud).
 
I Used To Think That Every Mario Game Was Just A Self Insert Fanfiction Written By Mario From Inside His Apartment In New Donk City. I Stopped Thinking That When I First Wrote A Fanfiction.
 
I think Luigi is partly jealous but he also doesn't mind lingering behind Mario because he's shy and he knows he's awkward. He usually lets Mario make all decisions for him even if Mario wants him to be more assertive. So as a result, this is why he's in his brother's shadow. He doesn't want to be seen as a failure, but he's also too afraid of failure to take the initiative so, that little shadow is like a comfort zone for him. Like Mario sheltering him.