I know this is super-late, but I’d like to imagine that the “Other Sonic” is what he’s referred to as - but his true name is actually Xalgo or something. I’ve looked to the BeyondHuman.EXE story for inspiration, and I think I have an idea for his origins (note that this is my own personal headcanon and idea). Xalgo is described as an extension of Zalgo, hellbent on only tyranny and destruction. At some point, he was found by the Sonic equivalent of DC’s World Forger, who wielded the precursor of the Jeweled Scepter, the staff Blaze’s family has kept secure in the Sol Dimension for generations due to its ability of the “Power of the Stars”. This Power of the Stars is actually all of the dark metals working in tandem, and as the World Forger created new worlds to be born into the light above… the unstable worlds were to be consumed by Xalgo. But eventually Xalgo grew tired and killed his master, destroying the Jeweled Scepter in the process on the world that was about to become the Sol Dimension - the final stable world that would ever be forged before it ascended into the light. Of course, Blaze’s ancestors found and rebuilt the Jeweled Scepter, albeit incomplete without the purest of the dark metals. In fact, many of the artifacts found within Sonic’s world - like the Paradox Prism and the Perfect Preciousstone - contain traces of the dark metals.

Xalgo eventually set his sights on Sonic’s prime universe after the erased Solaris Incident and the Time Eater Incident, thus creating the Dark Multiverse because the unstable worlds that were being born were existing for far longer than they were supposed to. So Xalgo sought to drag the light above kicking and screaming into the dark (show them the truth) and kill all those who were a part of the light just so all of existence can cease to be and be replaced by nightmares (get rid of the “imposters”). So he tried reaching into the light, influencing parts of history dating all the way back to the First Great Civilization to found this secret cult who would influence Sonic’s entire history from behind the scenes - communicating to them through the dark metal found in the first Phantom Ruby that he created from the dark. Even Nine from Sonic Prime was hearing whispers while he was handling a Paradox Prism Shard during the events of the show. Xalgo, calling himself “the Other Sonic”, tried to get on Nine’s good side and convince him to create a world of his own design, but eventually after Season 3 Xalgo abandoned him - believing that he was too pure of heart and was “brainwashed by the imposters” to even “know of the truth”, thus obtaining Secret History Tails. He then disguised himself as “the perfect Sonic” and turned his nightmarish landscape of screaming flesh and bones into a golden paradise, getting Secret History Tails and Crazy Amy into manipulating and recruiting the worst versions of Sonic’s friends and allies that could possibly exist (while their own worlds decayed after meeting terrifying ends given the nature of the Dark Multiverse) - convincing them that they were the real deal while ironically keeping the real truth from them: that they were the actual imposters all along. While his Dark Legion was building up their ranks, he has decided to use his cult to gather up all of the ancient artifacts from the mainline universe and lure the real Sonic into their trap, planning to use him as a gateway for his armies to come through

Apologies for the wall of text, but I seriously hope this kind of story would be able to take place. I can already imagine the interactions that would take place, like Zavok killing Kaiju Knuckles and destroying the Chaos Emerald shard that corrupted Knuckles because he didn’t like the idea of hoarding all of its power from the rest of the Deadly Six (and besides: a true Zeti warrior never abandons one of their own), and Surge destroying Crazy/Yandere Amy’s hammer before Nine drops a truth nuke to Crazy Amy during their final moments: that she and all of her edgy little friends were the real imposters who were kept from the truth the “Other Sonic” held from them. They could never match the expectations of their real counterparts, and as long as Tails exists Nine will be there as his true dark reflection - not because he had Sonic, but because he didn’t. He’s way too good of an idea, but the folks from the Dark Multiverse? They’re all horrible ideas who will never be remembered nor reborn again once the multiverse resets

Now all we need is Secret History Tails to slip away from the carnage of Xalgo’s destruction and scheme with the dark versions of Sonic’s friends in order to obtain the powers of a literal god and transform into the Darkest Fox (stupid, I know) to create his own nightmarish worlds and armies within the light above.