As spotted in Sonic X Shadow Generations' Movie Pack DLC, there's a reference to Eggman's appearance in Adventures of Sonic the Hedgehog - which makes sense since he's the centre of most of the ...

The game's story follows Sonic after he finds out about Dr Eggman's new plan to extract all the natural resources from an Mystical island. Face Metal Sonic and save the island, stop Eggman from ...