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

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

Yoshi and Birdo cosplaying as Ichigo Momomiya

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

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

The "Big Green Man" (Guest) teaser.

Despite being Water (Or Mutated Chao) slime sounds

Basically

Valgallah's Cream's "Chao Force" Super

Command is

D,DF,F X+Y

Father and Son love

(Advance 1) Angel Island Zone.

Originally for Infinite Battle Now retooled