"Lights out, Omega."
A Summary of Shadow's Arc in the Diamond Series
*****CONTAINS SPOILERS*****
Shadow in SatAM Goes BOOM
This is Modern Shadow as we know him, removed from his canon version of the Modern World, soon after Shadow the Hedgehog. He and Boom Sonic are brought to the SatAM world by Tikal to help the Freedom Fighters defeat Doctor Robotnik. Upon perishing at the hands of Snively's roboticized version of Robotinik, Tikal removes Shadow and places him into a Shadowless World.
Shadow in Shadowless World
Same Shadow as SatAM Goes BOOM! and again, brought here by Tikal to help defeat Doctor Robotnik. Following the sobering defeat of an evil version of Omega, Shadow remains in this dystopian world, at first reluctantly. Then, at Dystopian Modern Sonic's broken-hearted request, Shadow decides that staying is his duty. He remains here indefinitely, until we see him again in the series epilogue. He is deeply motivated by the death of Boom Sonic (also brought here by Tikal), who took a fetal blast to the back from Omega. His death shapes Shadow's sense of purpose in this world, similar to his resolved feelings about Maria.
Shadow in Fickle Hedgehog Village
While superficially, this is in fact Boom Shadow, we later learn in Infinite Sadness, that this is the original Shadow who died in the Dystopian Modern Universe, delivered by Tikal to what was initially, a Shadowless Boom Universe. We also learn that all of the Shadows in the series have the ability to share memories with one another via dreams or near death experiences. This can be confusing for these Shadows, which is why the Shadow we see in SatAM Goes BOOM! gets himself confused with the presumably deceased, Dystopian Shadow now living in the Boom Universe. Boom Shadow (who is actually Dystopian Shadow) dreams about what happened in the Shadowless World story. He also has a crush on Boom Sonic. This lines up with Dystopian Modern Sonic's heavier feelings for Shadow, blaming himself for his assumed death, as well as proclaiming to the replacement Shadow, that the loss broke his heart.
Shadow in Eggman VS Sonadow
This is the above Boom Shadow. In this story, Eggman manages to accidentally kill him. His death and all of the events that follow are then erased when Silver the Hedgehog (whom Eggman also simultaneously, accidentally brings into their world), goes back in time to undo Shadow's death. Ultimately, Silver ends getting killed instead, also accidentally and to Boom Eggman's great delight. We learn in this story that Silver is in fact Boom Shadow's son from the future, a secret that Boom Rouge hid in another dimension, one which includes Blaze and also eventually becomes dystopian. Though this is not the Dystopian Modern World we see in any of the other stories. We only see this world very briefly in the first chapter of Diamond in the Sky.
Shadow in Diamond in the Sky
Same Shadow in Fickle Hedgehog Village and Eggman VS Sonadow. He is devastated after witnessing Eggman slay his future son. He spends much of this story blaming himself for Silver's death, claiming he selfishly let Silver stay too long, making him vulnerable to Boom Eggman's faulty time machine. Unable to see through his own grief, Boom Sonic tries to convince him that Silver's death was one hundred precent Eggman's doing. When Rouge finally rescues both, another version of Silver and spirit of the departed Silver (combined), Shadow joyfully receives another chance to be happy again.
Shadow in Infinite Sadness
Boom Shadow/Departed Dystopian Shadow takes it upon himself to preserve a suffering Infinite, via Tikal's request. He sees himself in the tormented jackal, and quickly learns that Mephiles not only framed another Shadow for the demise of Jackal Squad, but that Mephiles then enslaved Infinite using the Phantom Ruby. Tikal tasks Shadow with giving the Damn Fourth Chaos Emerald to Infinite, which replaces the Phantom Ruby in Infinite's chest and gives him the ability to see his past life as "Anubis," who was best friends with Tikal. After Tikal fades away, assumedly forever, Shadow catches Infinite as he is plummeting to his death and tells him about Tikal catching him as he was falling at the end of Sonic Adventure 2. He tells Infinite he belongs in the Boom World (something that both Tikal and even Mephiles also reiterate through out the story). Infinite accepts himself as Boom Infinite/Anubis (in a past life), and becomes friends with Boom Shadow from this point on.
Shadow in Ghost in the Maze
By this point, Boom Shadow is known as Boom Sonic's partner, Silver's loving father, and Infinite's surrogate, older brother. He protects Infinite from the surprisingly threatening King Boom Boo, and encourages the jackal regarding a very real chance that Tikal may still be around. His theory is that Tikal was detached from her sleeping body and that the battle between Mephiles and Infinite Chaos in the previous story, may have resulted in her awakening. Though it's not discussed, in our improvisations, me and JakeyKoop have canonized that Chaos quite liked Zero and used their merged powers as Infinite Chaos to release Tikal from her slumber... so she could live a loving, protected life with a very powerful, reincarnated Anubis.
Shadow in Watch Dogs of the ARK
About 250 years after Shadowless World, Shadow is the only one that remains from his group of friends. Now living aboard the ARK, another version of Infinite (not the same one in Infinite Sadness), ends up flee-teleporting to the ARK following the canon events in Sonic Forces. Shadow almost instantly takes a loving interest in him, thinking he is a beautiful, female fox-girl. The two soon grow fondly of each other until one day, when Black Doom attacks the ARK and kills ARK Infinite. Infinite's death causes Shadow to finally break and beg to the abyss, that he should die too with his friends. Silver (not the Boom Silver from the previous stories), then defeats Black Doom after his spirit merges with the wisps. He hears Shadow's sorrowful request and uses his new powers as The Ultimate Life Force, to split Shadow's immortal life into two mortal lives, one for Shadow and one for a revived Infinite. Shadow then takes Infinite as his partner on the ARK, where they are able to anticipate a future together, celebrating that both friends will one day die at the same time.
