Sealed Evil in a Can

"Old folk saying: 'You can catch the devil, but you can't hold him long."

- Rod Serling, from The Twilight Zone (1959) episode "The Howling Man" Sealed Evil In A Can, as the title suggests, is a way to introduce a villain suddenly, especially one that is legendary and powerful. It also explains why the villain hasn't done anything up to that point: it just now escaped. Sometimes, the Big Bad's plan is to unseal the can of some ancient God of Evil, hoping they'll get some of that great power as a reward. If they succeed, it almost always turns out that the Sealed Evil was manipulating them into freeing them, making the Sealed Evil the true Big Bad. Sealed Evil™ almost never rewards those who release it. It may act like the malevolent flavor of a Jackass Genie, twisting their releasers' wishes back on them, or it may simply decide that You Have Outlived Your Usefulness. Remember: Evil Is Not a Toy.