Sometimes, the Big Bad is just too darned evil to be Sealed in a Can. Perhaps he already was, and it didn't work. After hammering him time and again, our hero eventually realizes that It's Up to Him, and carries out the Heroic Sacrifice Worse than Death: Trapping themselves in a duel with the bad guy for all eternity, thus effectively "sealing" their opponent with themselves as the plug. If they aren't strong enough, the baddy will escape, possibly using its would-be impediment as a Soul Jar. This can also be used as a Backstory, with the release of the Big Bad also releasing the original hero.