Sonic Adventure 2’s Last Scene — the final story segment, unlocked after completing both Hero and Dark stories — reveals Shadow’s true history: Gerald Robotnik’s diary, the Biolizard project, and Maria’s final wish. It also reveals that the Shadow the player defeated in the Dark story was not the ‘real’ Shadow in any meaningful sense — he had been operating on a programmed memory of hatred that overrode his actual directive.
What the Last Scene adds that most players remember only vaguely: Gerald Robotnik’s final television broadcast, recorded before his execution, in which he describes humanity as beyond redemption and announces that he has programmed the ARK’s cannon to destroy Earth as his revenge. This broadcast is framed as a villain’s monologue — but read carefully, it is also a grief document. Gerald lost Maria, then lost his mind, then lost everything, and his final act is the only thing left to him that feels like justice.
Sonic Team built a tragedy inside a Sonic game in 2001. The Last Scene earned the series its reputation for attempting genuine emotional stakes, unevenly but seriously.

Found this by accident on my third run. Came here to understand what I was actually looking at. Great write-up.
Saved this article for my gaming reference folder. Essential reading for anyone serious about this game.