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How about a trope for how action rises in a show's final season? I'm thinking right now of the last few episodes of LOST and TheSopranos. The Big Bad has either achieved true power or finally become genuinely pissed and unleashes his fury upon the cast. Several main characters die -- now that the show's over, we no longer have to worry about which characters are necessary to keep the show going. In LOST, the Man in Black was free and on the move. He killed dozens of Redshirts, then Sayid, Sun, Jin, and ultimately Jack.. In TheSopranos, Phil Leotardo was rising in the ranks of the Lupertazzi family and growing progressively more angry at Tony as the season rolled on. Then he finally takes command when John Sacrimoni dies and he sends assassins after Sil, Bobby and Tony. In TheX-Files, though they didn't necessarily know the 9th season was the last, they brought in the super soldiers, a whole new alien threat even more invincible than the last. And they killed the Gunmen, too. Serenity is kind of the grand finale of Firefly. Certainly more action, and a devastating amount of character death. This would be an Ending Trope, and it would have ties to Trash the Set, Apocalypse Wow, and others.