SPOILERS FOR SONIC SUPERSTARS DO NOT READ IF YOU HAVEN'T FINISHED THE GAME. Quoting here: It is believed that Great Dark Dragon was created as a sort of nod off of lore exclusive to the Japanese version of Sonic 3, where it is stated that Knuckles mistakes the Death Egg for the egg of a dragon, said to cause misfortune for all. This idea would have served as the game's true final boss, but was ultimately scrapped. It is also implied that Great Dark Dragon may be connected in some way to The End due to the mural found in the ruins that Eggman, Fang, and Trip explore in the prologue showing a purplish celestial body in the center of it containing the dragon. It should be STRESSED however that this is all speculation.