OOH THE JOY. I might forget some because I’ve had a lot over the course of the past four years, but…

He’s about a few days to a week old chronologically (although this is already implied canonically)
He’s an older teenager mentally (my old range was 16-19 iirc)
He does not actually care at all about his gender or what people see him as; he’s male but also an enigma (maybe a tad non-binary)
He’s wasian!! White and Japanese
Him and Olivia are twins, so no age gap between them
He’s gay and panaesthetic (meaning he’s aesthetically attracted to all genders— admiring someone and enjoying the sight of them without being attracted to them in a romantic or sexual way)
^ That being said, he’s nearly incapable of romantic relationships, finding no interest in anyone around him aside from thinking “Oh, they look nice. They’d be nice to stare at (Peach).”
This one is more recent but I’ve started to hc him as having NPD, or potentially any other cluster B personality disorder
He doesn’t care much about the LoS as people, only seeing them as pawns
In my AU where he’s revived, he’s still uncomfortable around the Origami Craftsman, but he wishes things could be better between them (as now he’s realized the misunderstanding of the writing on his stomach)
He cares deeply for Olivia (post-canon AU) although she scolds him quite a bit as he still struggles to keep his emotions under control and has still impulsively used his powers for no good (eg. trapping people who annoy him in walls)
He has an ethereal and semi-androgynous, breathy voice, that can switch quickly to a deeper growl when yelling
He enjoys reading books and learning about the world from them, although he’s still uneducated (much like Olivia)
He has similar speech patterns to Olivia, saying “Ooh” like her, making puns (he thinks they make him seem cool), and sometimes rhyming like speaking in poems (he also thinks this makes him seem cool) (although this is semi-canon as he does vaguely share these features with Olivia already)
He acts mature, high and mighty, pretentious— but when angered, his mind jumbles up in rage and instead he blurts out insults, many of which make him sound childish (although this is also semi-canon)
He’s surprisingly amazing at singing, with an angelic voice unmatched by none other than Olivia
This one is an older hc (2021), but while he’s great at origami, he sucks at painting or drawing
He likes Colored Pencils’s artwork, though, and may have it do work for him
A lot of NPCs such as shy guys and the like distantly admire him for his beauty
He has a strange attraction (non-romantic/sexual) towards Mario, finding him beautiful and strong— the ideal man, but one he wants to watch crumble as they have opposing views (this is semi-canon? In Japanese he admires Mario’s strength and in English he admires his striking colors, while also teasingly complimenting him, likely as a way to get under his skin (“You made it here. As expected of Mario.”))
He hates having his hairstyle mocked or insulted
In the end of it all, he’s an imperfect being: made to be the perfect display of what origami is capable of, but “tainted” and set along the wrong path as a result of the lack of care given to him as a person rather than a sheet of paper. He is capable of many good things, but he has a long way to go, and with the right help and role models, he can improve himself and be accepted by society, even as someone who caused much hurt to others.
(I also have the post-canon AU where he’s “forced” to live with Peach in the castle and must learn from her and Mario to become a hero instead of a villain, with the help of Olivia who lives with him now)

YA!!!!!! I probably (definitely) have more I could talk about but those are kind of the basics I think. I tried to keep it all limited to his canon design rather than his human one, as they’re slightly different with headcanons and facts ………… so THANK YOU FOR THE QUESTION I HAD FUN WITH THIS ONE