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Tear Jerker: Sonic Unleashed
Sonic's humiliating defeat in the intro.
Chip's resealing into the Earth. To make things worse, Sonic is completely stoic.
During the credits of Sonic Unleashed, the song "Dear My Friend". It's almost kind of a Mood Whiplash since the rest of the game seemed kind of light-hearted, (with Aside Glances, all kinds of little gags during the cutscenes, the cartoony-looking villagers, not to mention the funny promo short: "Night of the Werehog,") then comes the Bittersweet Ending. What really brings it out is the fact that the song is supposedly in Chip's POV, and you know he and Sonic will never see each other again.