So the Classic Sonic series (or the Origins series) every game has new characters, like:

Sonic 1:Sonic

Sonic CD:Metal Sonic & Amy

Sonic 2:Tails & Mecha Sonic mk.I

Sonic 3:Knuckles

Sonic & Knuckles:Mecha Sonic mk.II

We know Sonic 4 introduced Metal Sonic in Episode II, but Metal already appeared in CD. So what character do you think can be a good fit if Sonic 4 had a new character? (Modern Characters only)