Sumin didnt just make some characters But also sandbag (Though bare bones)

Silver (With A Counter move with a cost of Power) and Metal Sonic

(Advance 1) Angel Island Zone.

Originally for Infinite Battle Now retooled

Giving the character's Icons some polish.

(Will be in the next update)

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

(coming some time soon or something.) The 1st Sonic Battle Redux arcade Run: Sonic.

Despite being Water (Or Mutated Chao) slime sounds

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

Basically

Valgallah's Cream's "Chao Force" Super

Command is

D,DF,F X+Y

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