2/3 of them are references to

Sonic's Concept and is also a Skin in Sonic Superstars Cream's Debut (Though inconsistent looks)

A former 90s rival's (A red capped plumber guy) recent 3D platformer since 2017

surprising how i manage to draw King K. Rool accurately like that for the first time

Every Continue and Confirming

As of 6/26/2022

Another mechanic that I coded for the first time

"Grab Canceling"

The only thing that varies between character is: how long will they actually throw the opponent while Pressing Y + Holding FWD/Pressing Z + Holding Backwards will still do the cancel trick

Yoshi and Birdo cosplaying as Ichigo Momomiya

A returning move from Infinite Battle

but a bit more on Sonic 06's Green Gem.

Act Music as Rounds? (may not apply to every stage)

The "Big Green Man" (Guest) teaser.

Early previews of "Shining Wine (Not alcohol)" and "Castle Party"

I'm taking you down like its 1998/1999!