Continuing where I left off, I think I have a decent Classic Sonic game timeline. Most are fine just in release order with the only shifts being due to Metal Sonic being a singular entity and not just multiple hedgehog robots.

Sonic the Hedgehog
Sonic the Hedgehog CD
Tails Adventure
Sonic the Hedgehog 2
Sonic the Hedgehog 3&K (Sonic & Tails story)
Sonic the Hedgehog 3&K (Knuckles story)
Sonic Chaos
Sonic Drift (Chaos GP)
Sonic Spinball
Sonic Labyrinth
Sonic Mania
Sonic Mania Plus
Knuckles Chaotix (birth of Metal Sonic Kai)
Sonic Triple Trouble
Sonic Drift 2 (Chaos GP 2)
Sonic Blast
Sonic R (World Grand Prix)
Tails Skypatrol
Sonic 3d Blast
Sonic the Fighters
Sonic Superstars
Sonic Superstars (Trip's Story and Last Story)

Tails Adventure is the oddball out due to Sonic Origins (he only started flying after meeting Sonic). Also the game gear games run on the logic that there are only six emeralds for some reason. Even post-Sonic 2 games run on this.

>>535252327
Because "Metal Sonic" is meant to be a singular character. Here's a QRD:

Sonic CD: Metal Sonic appears, gets his ass kicked, his corpse is left on Little Planet.
Sonic Mania: Eggman recovers Metal with the help of the Phantom Ruby. Metal gets his ass kicked again, is left on Little Planet.
Sonic 4: Eggman recovers Metal Sonic from Little Planet (again), supes him up by shoving a Purple orb up his exhaust pipe, loses to Sonic and Tails (again) but this time Eggman recovers him.
Sonic Adventure: Metal Sonic is seen recovering in a pod with Mecha Sonic 1 & 2.

Now, Knuckles Chaotix on its own explains this by claiming Eggman recovered Metal Sonic CPUs and put him in a new body (Metal Sonic Kai) hence why he was around for Fighters, Drift 2, and Triple Trouble. Sonic Mania doesn't conflict with this so long as it happens BEFORE Chaotix. Sonic 4 however, being a Modern game, does as it must come after in the Modern era.

That is the issue. Either Chaotix and all the non-Sonic Team Classic games go or Sonic 4 (which has Sonic Team's logo on it despite being made by Dimps) goes....And Sonic Team ain't gonna allow that.

>>533913059
Just so we're clear, Metal Sonic itself is just called "Metal Sonic Kai" in this game.