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

The "Big Green Man" (Guest) teaser.

Every Continue and Confirming

As of 6/26/2022

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

Another returning move For Amy Rose Amy Flash.

(Advance 1) Angel Island Zone.

Originally for Infinite Battle Now retooled

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

A returning move from Infinite Battle

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

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

Despite being Water (Or Mutated Chao) slime sounds