Marine, Sticks, Trip and Metal Knuckles.

IDW Exclusive Characters go far because they are plenty and exclusive

Starline was killed off, I don’t see him appearing anymore in future games/updates/content.

And Super Sonic 2 (I’m still calling him that) is basically just Super Sonic but with blue eyes and all the good stuff increased by 4.

I'd like to see Kit, Rough and Tumble. If they add Trip they should add the other retro characters too.

@FunniMemeBoi2023 Gamma's playable, so I don't think death would be much of an impediment.

Maybe he was repaired for Speed Battle.

I don't see how they’d revive Starline after he got absolutely FLATTENED,

Now that I think about it, it IS kind of odd that they put in Surge but not Kit.

Also the files say "Super Sonic 2" but Flynn said the "internal" term for him - probably something in the script for Final Horizon or something - was "Starfall Super Sonic", but neither one are official.

@FunniMemeBoi2023 Well, Mephiles and Infinite are playable despite being erased from existence, so I think someone who was killed conventionally like Starline can still appear.

…

Crap, I forgot Mephiles and Infinite died and were resurrected for Speed Battle…

@CyberSonic6096324.0 Morio Kishimoto said there's a chance of Infinite returning, which suggests he's alive and well.

But he also said that Mephiles could return at some point, who was wiped from the timeline.

Yes, but Infinite wasn't.