This is my headcanon, though it may make a few references beyond the 4th wall though and only focusing on the main fighters (So no spirits or assist trophies). Here's to hoping I still have a creative touch here.
The Smash Roster lives in what could be described as a large tower building in an apartment style within the realm between universes, ran by two specific individuals who can detach their hands respectively (hence Master and Crazy Hand), and are the ones responsible for sending out invitations to those they deem worthy of the Super Smash Bros. competition they hold annually, to see who's the strongest.
Thus far those who have taken the champion title are
![Fox :ultfox: :ultfox:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Meta Knight :ultmetaknight: :ultmetaknight:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, and
![Bayonetta :ultbayonetta: :ultbayonetta:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, though everyone seems to have upped their game, so there's no idea who will take it now.
As for what goes on between the fighters, there's a lot to unpack here:
![Mario :ultmario: :ultmario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Sonic :ultsonic: :ultsonic:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
were at one time fierce rivals, and still are in the ring, but outside of the ring, they've gotten along much better, but still have that competitive vibe between the two in nearly everything. The rivalry, even if only perceived, has become famous not just in the roster, but supposedly the entire multiverse as well.
![Link :ultlink: :ultlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Cloud :ultcloud: :ultcloud:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
have a similar thing going on, only this time they always were friends, but they constantly wonder who's the better of the other. Recently though, Ike has also been caught in this, leading to them constantly fighting to figure out whose the best out of the three, especially in the ring.
![Palutena :ultpalutena: :ultpalutena:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
supposedly made a few enemies with the other girls, most notably with
![Zelda :ultzelda: :ultzelda:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Bayonetta :ultbayonetta: :ultbayonetta:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, and
![Lucina :ultlucina: :ultlucina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
. However, only one of those is true, as she gets along very well with
![Lucina :ultlucina: :ultlucina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, whom she treats like a little sister at times.
![Bayonetta :ultbayonetta: :ultbayonetta:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
though, they like to play upon the two being rivals of sorts as well as use such to scare the hell out of
![Pit :ultpit: :ultpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, but in reality they like to have girl's night outs on occasion. It's with
![Zelda :ultzelda: :ultzelda:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
she's on bad terms with, as she supposedly tried to steal
![Link :ultlink: :ultlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
from her, which led to the two having a large squabble that
![Pit :ultpit: :ultpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Mario :ultmario: :ultmario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
had to break up. This led to the two not showing each other mercy in the ring since.
![Pit :ultpit: :ultpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
doesn't say it fully, but he actually has a bit of a crush on
![Lucina :ultlucina: :ultlucina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, though he can't spit it out as he's too nervous. Also he's often picked on about being a Momma's boy by some of the others.
![Pit :ultpit: :ultpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
also is deathly afraid of
![Bayonetta :ultbayonetta: :ultbayonetta:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, due to her reputation as an Angel-Killer.
![Dark Pit :ultdarkpit: :ultdarkpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
often calls him a baby for this, despite him actually being just as terrified of her deep down.
![Pikachu :ultpikachu: :ultpikachu:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Jigglypuff :ultjigglypuff: :ultjigglypuff:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
are actually the Pokemon of two very skilled trainers who are top players at a certain fighting game, and are actually not in the ring when their pokemon enter it, rather they are outside of it. (Cookie to those who guess who I'm referring to).
![Greninja :ultgreninja: :ultgreninja:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Incineroar :ultincineroar: :ultincineroar:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
has sort of the same thing going on, except their trainers are busy most of the time.
![Pokemon Trainer :ultpokemontrainer: :ultpokemontrainer:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Pokemon Trainer (Female) :ultpokemontrainerf: :ultpokemontrainerf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
are actually a couple, who love Pokemon battles, often swapping each other out in order to enjoy it to the max.
![Luigi :ultluigi: :ultluigi:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
used to spend his days alone, trying to make himself braver and better his skills. This backfired when he nearly died, but was saved by
![Simon Belmont :ultsimon: :ultsimon:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
. Ever since then, he's looked up to Simon, hoping to gain the courage to thank him as well.
![Mario :ultmario: :ultmario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Dr. Mario :ultdoc: :ultdoc:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
are from alternate universes, the main difference being from had
![Mario :ultmario: :ultmario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
pursued his medical degree instead of going the Mushroom Kingdom for the first time, an apparently life-changing decision.
![Wario :ultwario: :ultwario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is actually the reason why Waluigi is not in the Roster, as the high powers along with many others believe that the duo would cause too much trouble, given
![Wario :ultwario: :ultwario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
has a massive gas problem, especially with how he managed to weaponize his farts.
![Marth :ultmarth: :ultmarth:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is still trying to learn english, so he sounds weird sometimes when he speaks it. He's glad that
![Roy :ultroy: :ultroy:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is back though, especially since he feels like he had something to do with him being expelled from the roster for awhile.
![Chrom :ultchrom: :ultchrom:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
got into the roster thanks to
![Robin (Female) :ultrobinf: :ultrobinf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, though given
![Robin (Female) :ultrobinf: :ultrobinf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
has found herself struggling even more since her husband joined, though
![Chrom :ultchrom: :ultchrom:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
himself is taking the competition by storm. It's due to this, that many of the other fighters have gone under the assumption that
![Robin (Female) :ultrobinf: :ultrobinf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
was very reliant on her husband to excel in the competition.
![Lucina :ultlucina: :ultlucina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
may seem polite on the surface, but she actually has a bit of a sailor mouth when she gets too angry, and she basically becomes another person in these scenarios. It actually scares some of the other fighters.
![Link :ultlink: :ultlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Young Link :ultyounglink: :ultyounglink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, and
![Toon Link :ulttoonlink: :ulttoonlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
act in such kindred spirit some of the other fighters think they are brothers. This just confuses them for the most part.
![Toon Link :ulttoonlink: :ulttoonlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
also HATES being called short.
![Link :ultlink: :ultlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
also has a bad habit of overeating too, actually on par with
![King Dedede :ultkingdedede: :ultkingdedede:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Wario :ultwario: :ultwario:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
in that regard.
![Roy :ultroy: :ultroy:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Daisy :ultdaisy: :ultdaisy:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Falco :ultfalco: :ultfalco:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, and
![Dark Pit :ultdarkpit: :ultdarkpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
also love playing D&D and Pathfinder on Saturdays. Sometimes
![Toon Link :ulttoonlink: :ulttoonlink:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Pit :ultpit: :ultpit:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
join in though, and it makes things very hectic.
![Lucas :ultlucas: :ultlucas:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is extremely attached to
![Rosalina & Luma :ultrosalina: :ultrosalina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, though as to why it's best not to say why.
![Rosalina & Luma :ultrosalina: :ultrosalina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
doesn't mind a bit either, as she acts like a surrogate mom to
![Lucas :ultlucas: :ultlucas:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
,
![Ness :ultness: :ultness:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
, and
![Bowser Jr. :ultbowserjr: :ultbowserjr:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is often a prankster, usually in conjunction with
![Inkling :ultinkling: :ultinkling:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
.
![Bowser Jr. :ultbowserjr: :ultbowserjr:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is also extremely convinced that
![Corrin (Female) :ultcorrinf: :ultcorrinf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
is his mom given she is a dragon herself, often leading to awkward moments that she's annoyed, yet flattered by.
And of course,
![Isabelle :ultisabelle: :ultisabelle:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
just goes around helping everyone with things and keeping the place tidy. Rumor has it though that she was put into the roster by accident, but the powers-that-be decided to keep her in there as a joke. She's also unintentionally the one responsible for the rumor flying around about
![Villager :ultvillager: :ultvillager:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
's dark secrets.
I'll probably have more in the future.